Exactly. Everything that the yeast transport through the cell wall into the beer is a waste product. The stuff they “want” stays in the cell.
isn’t secretion when you keep something to yourself?
Secretion, as I understand it serves a purpose for the secretor and excretion is waste.
That doesn’t mean one critter’s waste isn’t another critter’s wassail.
+1 Mutually beneficial relationship - we get the yeast fat on sugar, they provide the party. 
The way I understand it, excreted is not necessarily good for anyone. Secreted is usually good for at least one.
Well, ya but I wasn’t going to say it.