From personal experience...having condition in green is when I've seen my players performing well...tracked via match ratings.
For the first 15 odd seasons...I'd always start with around 70% condition on my players...I won mostly...but players performance varied a lot... consistency was missing.
After moving to a regime where I have at least 80% condition...mostly above 90% at start of match...the results, performance and ratings are more consistent.
I am able to progress through to semis and finals of cups and cl playing against+1 opponents always....win the league.
Playing with low condition is just a risk. You got to pray RNG favors you or opponent is also at lower condition.
If you have the greens...use them.
If not, well, there's not much option you have.