I personally like it in larger groups (full party to alliance) when waymarks are marked so you can quickly parse locations and directions with barely a glance and I like it when the tank and healers are marked so it is easier to keep track of where everyone is.

As far as people turning them on and off, sometimes people do that because they think that where they want the waymarks is the only correct spot even when the difference is negligible, otherwise trolls just be trolling.