A build saver would definitely be great for the multiple game modes within the game as well as having multiple builds within the game mode itself.
For SPvP, it’d be great to save multiple trait and gear sets to go along with them instead of having to switch out all the time for different group comps.
For WvW and PvE, I’m sure people also have different builds for dungeoneering, small party roaming, large squad based combat, etc. It’d be great to have a build saver for all of that.