To add to my post above:

There is no point having lots of subs if you don't use them because - as Gaz pointed out, morale will drop. In my last three seasons I've got to two cup and two CL finals, in the same seasons. So I had two game days almost everyday. Everyone in my squad played at least twenty games and the quality difference between the 'best' eleven and reserves is minimal

I found that I rarely needed to use blue or green boosters, which is good seeing as you can't get them through offers at the moment

So, with a 22 man squad;

Pros - don't have to use boosters, always have a reserve for injuries, more players equals more options for formations or if a player is not playing well

Con - can't add your youths (who aren't good enough anyway, usually)

Pro/Con - the value and quality of your players must be even within the squad, so you have less money for 'superstars'. That being said, it also means that all your players are equally good so you aren't relying on a few and it doesn't matter if your 'best' players get injured