Yes, that goes without saying; 100% water changes are ideal, however, realistically even the most dedicated among us would be hard pressed to guarantee almost exact same temperature of replacement water along with guaranteed low contaminants, making it an unrealistic option...
Don't get me wrong, I've heard of many members who do massive water changes regularly; with no problems and healthy stock. I've also read threads about people who've had their entire tanks crash and all fish die, after doing such changes
Plus, to echo
P
predatorkeeper87
i personally never want to be in the position that I need to do 80% water change just to maintain my water parameters, I like having margin for error so that lets say I have to go abroad for two weeks; my levels will still be fine at the end of two weeks, and not having to rely on someone else to look after my tanks etc.
Personal preference
P.S also a final somewhat controversial point to add, on tanks that I've performed only minimal water changes over a long period of time; I've had some very large growing healthy fish. Perhaps there is something to be said about aged water, but its just a thought; really not ready to open up that can of worms haha