My suggestion is always keep your Squad full 22 players, why?
1. To maximize the condition you can generate a day. 40% x 22 better than 40% x 17 tho.
2. You can effectively rotate your squad to play friendlies and earn green + red pack as well as let your focus-training player to train and play extra game.
3. This reason seem not to be fair, but having some low quality players in your team is actually good for you, your opponent (or T11 system) perhaps underestimate you (and drawn you in a bit less difficult Cup)
of course keeping these bad players won't cost you high wages since they aren't high quality. As long as they ain't your first 11, no harm but good. And you can always sell or sack them since your squad full 22 but you can have better ones
I don't know how everyone manage the team condition but for me I divide my 22 players Squad into 4 groups.
A: Training Group: 3-5 players (more or less depend on your team) consistently trained and play as much as possible. They must be 18-21 fast trained players. Green Packs after cover your main squad, are most used for this group. These player may be in first 11 maybe Sub depend on their quality (standard good enough) or performance. Watch out, injuries occurs this group the most.
B: The First 11 except group A. Always play important matches, they are good/great player, may not be young and fast trainers so only train them if they have spare condition (95%+ for matches) and rarely generate their condition using green pack unless you have 2, 3 matches one after another..
C: The Second 11. They are team to play friendlies. group A + other donkeys (reserve or sub but not often used or be sub in). The purpose is to suck all their condition up in exchange for green packs and red packs, try to win and take no card
D: The rest of the team excluding A. B. They maybe some player you bought + slowly natural train (Role, sa) for selling back, keep for better Cup drawn, some time use them in group C as well.