Teapot-wise, that is.
Think about it. The more water you put into a pot, the hotter it will stay. A smaller amount of water will cool faster, even if you warm the pot first. This will affect the way that the tea brews when you put it into the pot. Even if a tea is meant to be brewed with water that has just come to a full boil, it is not meant to be kept at that temperature but to cool gradually as it steeps. This is why it is not recommended to place a tea cosy over your teapot while the leaves are still in there; the tea will stew.
I also think it is why some teas do not taste as good when brewed in a larger pot (much as I love my 6-8 cup London Pottery teapot, seen here coyly wearing its tea-cosy [tea-leaf free], it is better suited to herbal and robust black teas rather than anything more delicate).
Sometimes even brewing a two-cup pot rather than a single-cup pot can make a difference; I feel that the delicious Keemun from SanTion tastes better only brewed a single cup at a time, for example. Have you had a similar experience with the teas that you drink?