The Premier League is a physically and mentally draining division. It takes its toll on all players, and squads that are too small or fragile can be chewed up and spat out.
Although a strong and consistent core of players in the starting lineup is essential, substitutes who can make a difference with their fresh legs or easily slot into the team for the occasional match are just as important.
When injuries come into play, substitutes can play a massive role in the course of a season. Divock Origi played the hero in Liverpool's Champions League campaign and earned himself a long-term contract as a result. Many will be hoping to follow suit and make a name for themselves off the bench.
Here is how the top six's benches compare to one another as the new season nears.
Average Bench: Martinez, Holding, Maitland-Niles, Guendouzi, Ozil, Nelson, Martinelli
Unai Emery has struggled in the transfer window so far. However, with the signings of Kieran Tierney, Dani Cabellos, and Wilfred Zaha all still possible, the Spaniard's bench could be looking very different come August.
At the moment, however, the defence looks especially shaky. No replacement for Petr Cech means Emiliano Martinez will most likely play second fiddle to Bernd Leno. To make matters worse, there has been no defensive signings. The return of Rob Holding from injury and Callum Chambers from a loan spell at Fulham will provide some depth, however.
Going forward the Arsenal bench will look increasingly young. The likes of Joe Willock, Reiss Nelson, and Eddie Nketiah will all be fighting for a place on a bench that will most likely be shared with the increasingly outcast Mesut Ozil.
Squad Depth Rating: 5/10
5. Man Utd
Average Bench: Romero, Smalling, Young, McTominay, Lingard, James, Sanchez
Ole Gunnar Solskjaer's problems seem to be the opposite of those at the Emirates. Although the quality of players can be debated, a whole new side could be made out of the backup defenders at Solskjaer's disposal. The mix of youth and experience shown by Diogo Dalot fighting to share the bench with Chris Smalling and Ashley Young could be beneficial at Old Trafford.
On paper, the addition of Daniel James to a substitutes bench possibly consisting of Alexis Sanchez and Romelu Lukaku is extremely exciting. However, big players have struggled to make an impact of late at Utd when they have been asked to slot back into the first team.
It is clear that the Red Devils have more firepower in their squad than the Gunners but the squad has failed to reach its potential so far at Old Trafford.
Squad Depth Rating: 6/10
Average Bench: Gazzaniga, Foyth, Sanchez, Winks, Dier, Lamela, Moura
If Tottenham's bench consisted of seven Son Heung-Min's and Lucas Moura's then they would top this list. However, it does not.
The departure of Kieran Trippier has exposed some gaps that Mauricio Pochettino desperately needs to fill, even more so if Danny Rose also leaves the club as expected. Spurs are down to bare bones if they suffer a few injuries at the back, with Juan Foyth likely sharing the bench with whoever doesn't start out of Jan Vertongen and Davinson Sanchez.
The Tottenham bench, however, does get much stronger. The likes of Erik Lamela, Moura, and Son can make a huge difference to any match if they don't start. Although, Fernando Llorente and the occasional big goal he could produce will be missed unless a backup striker is signed.
Squad Depth Rating: 6.5/10
Average Bench: Mignolet, Matip, Milner, Keita, Oxlade-Chamberlain, Shaqiri, Brewster
The starting lineup is so strong at Liverpool that they hardly ever need to use their squad, bar from Jurgen Klopp's occasional shuffle of the midfield three. However, when they did need it players such as Divock Origi and Xherdan Shaqiri proved their worth.
The signing of Sepp van den Berg will help give a little more assurance to Klopp's defence if something were to happen to Virgil van Dijk, with Joe Gomez probably keeping Joel Matip on the bench too.
The return of Alex Oxlade-Chamberlain will definitely create fierce competition in the Liverpool midfield. Origi will be looking over his shoulder to Rhian Brewster who's been on fire so far this summer.
Squad Depth Rating: 7/10
Average Bench: Caballero, Alonso, Zouma, Barkley, Loftus-Cheek, Hudson-Odoi, Willian
With Frank Lampard at the helm it looks like the youth will be getting opportunities to impress at Stamford Bridge. Mason Mount, Tammy Abraham, and Callum Hudson-Odoi will all be hoping to build a relationship with the new boss and even start some games. However, the first two especially will most likely have to work their way up from the bench.
The transfer ban shouldn't trouble Lampard too much due to the existing talent in the squad. Kenedy seems to have made a statement in pre-season and could join the matchday squad alongside existing rotators Ross Barkley and Ruben Loftus-Cheek.
At the back, Kurt Zouma could remain a Chelsea player and challenge the likes of David Luiz for a spot on the starting lineup, keeping Andreas Christensen on the bench. On paper, Chelsea's squad depth is much stronger than most of the other top six sides, and that's without even mentioning super-sub Olivier Giroud.
Squad Depth Rating: 7.5/10
1. Man City
Average Bench: Bravo, Zinchenko, Otamendi, David Silva, Foden, Mahrez, Jesus
There's no two ways to go about it, the talent at the Etihad is ridiculous, and that includes those sat on the bench. Pep Guardiola could field a title challenging side out of his reserves. The battle to make it even onto the matchday squad is intense.
At the back, the Citizens will have a top sub keeper in Claudio Bravo, backed by the likes of Danilo, Nicolas Otamendi, and Oleksandr Zinchenko - all of whom could make the Arsenal starting lineup.
The further up the pitch, the better it gets for Guardiola. Bernado Silva will increasingly keep David Silva out of the starting lineup. Thus, the Spaniard will join Riyad Mahrez, Phil Foden, and Gabriel Jesus to watch their side score goal after goal. Leroy Sane will also have a huge part to play if he stays in Manchester.
Squad Depth Rating: 9/10
Source : 90min