Making too many substitutions in a game is bad or not?

My question is simple, but might have different answers from different players. I wonder what is your opinion about making too many substitutions in a game? It might be in a way that making all the substitutions at once, or one by one. Since with the rules in this year, we can make 5 substitutions in most of the leagues. I am playing an Atalanta save in Serie A in Italy which is not going very well, and i am really wondering if using all of those substitutions quite early (minute 55-75) somehow affects the players on the pitch on a bad way? Or is it vise versa? Indeed replacing a tired dude with a fresh one should be a good thing, but is it really for the most of the cases? Should i make those changes at 3 different change like 1-2-2 or should i make more changes at once like 1-3-1 or something like 4-1 or should i not use more than 3 subs if team is doing ok.

Sub players with 63% on fitness (maybe little below orange for FM21) as a general rule. If you are winning by two goals then more subs to keep the important players for next game.

I generally use all my subs around the 70th minute, but in the first season you can do like 3 subs and leave 1-2 for the final minutes.
It could be good or bad, depends on the player and situation, I do like the 5 subs cause my players can get more playing time but beyond the first season you wont have to worry about this

I am mostly losing ( :() ) so is it good to make more substitions before min 60 or is it bad and not helping the team at all? And While talking about going little below orange fitness is about 63%, my players usually seeing reds at the last minutes of the game which is around what % in FM20 i wonder? Because since this new fitness system is released with the FM21 i wonder what is what and if my players are actually getting tired before they normally should or not since i can not make comparisons with the last year.

Depends on match situation and time I guess ...

...winning by 2 goals ...all subs at once by fitness condition but preferably not the CBs round about 65-75 minute mark

Winning 1-0 pick the players with rating below 7.00 or fitness in red zone...2 subs ...max 3

winning by 3 goals sub all

losing 1-0 - 2 subs for worse performers if main striker has missed alot sub him if 65 mins up already

losing 2-0 - 2 subs if under 65 mins gone

losing 3-0 - sub all one time

take into account:

match situation =wining or losing or drawing
time = 1st half or second half....last quarter
player ratings
condition of players
player contract agreements
player fitness/match sharpness
Yellow Cards

2020-12-10 21:52#279791 cena : Depends on match situation and time I guess ...

...winning by 2 goals ...all subs at once by fitness condition but preferably not the CBs round about 65-75 minute mark

Winning 1-0 pick the players with rating below 7.00 or fitness in red zone...2 subs ...max 3

winning by 3 goals sub all

losing 1-0 - 2 subs for worse performers if main striker has missed alot sub him if 65 mins up already

losing 2-0 - 2 subs if under 65 mins gone

losing 3-0 - sub all one time

take into account:

match situation =wining or losing or drawing
time = 1st half or second half....last quarter
player ratings
condition of players
player contract agreements
player fitness/match sharpness
Yellow Cards

Thanks for recommendations. Can we simply say that making too many subs at once usually effect the team negatively?