There is a problem for managers, they know who they want to move on, but if the player is under contract, or no one else wants that player, it can be hard to move them on. Starting team selection and subs gives a pretty clear idea of the manager's preferences, so if a player keeps missing out on game time they should pick up the hint they are not a big part of the manager's plans, and then aim to move to somewhere else where they are more central.

As the season goes on a manager gets an idea of players' technical weaknesses, or issues over their character, that one just wouldn't know from training, or trials, or friendlies, until they play in highly competitive league matches, where any flaws get relentlessly revealed. I enjoy the quality of this league so much, as if we make mistakes the opponents are so good they take advantage, and that means we have to improve to cut out mistakes. It is sink or swim, no time to carry passengers. Thanks for feedback about keeping posts shorter, hopefully you can see I am trying my best to do that now!