I have the same question. I was watching Scarra play and he said he was buying up a champion to take it out of the champion pool. So if I am understanding this correctly, if I buy up 3 Garens to make one 2 Star Garen this will make Garen less likely to show up for other people because there are only 6 left in the pool of champions?
Edit: To make my question more specific since it is similar to a question answered in "Welcome to Teamfight Tactics! ...What is it?"
Is each champion limited to 9 total in the pool? So if I have a 3 star Garen is it now impossible for anyone to find even just one more Garen until I sell it or am eliminated and the Garens go back into the champion pool?