The current tagger tool is not very useful and is almost never used, However I think 2 different types of tagger tools could be very useful.
Player Tagger
Basically works the same as the current tagger tool, but allows you to mark players instead of bosses/mobs.
Ground Tagger
This I believe would be the most useful, it would allow you to place markers on specific points on the ground.
That way you can mark spawn locations, where people should stand, where the boss will be, etc.
These could be added as separate items, or be added onto the current tagger tool which marks enemies. However, I feel the easiest intuitive implementation would probably be to have them all as separate tools.