Does a team need more than 25 players over 21?

[drivin_me_nuts]

OK, so i'm not a big football fan and I caught this on the news yesterday that some in the Premiership are not to pleased at their squad size being limited to 25 over 21's and 8 homegrown players.

Naive question here - other than 'cos we can', is there a logical reason why a team might need/want to have more than 25 players?