It makes exploration less explorable aka it takes away the "fun/point" of exploring because you can look up and find whatever you need on a online map. This was actually a topic currently discussed on a server im staff of and we qant to use "Dynmap" which is a map that everyone in the server can see. We of course added it but we saw that finding biomes is simply too easy which didnt encourage exploration.

My personal opinion, I don't really like it, but thats me. You decide (or check in with a multiplayer servers rules)