It depends on the profession/build how much you can benefit from Celestial Gear. Obviously Hybrid builds benefit the most. In Open World and Story Misssion builds suited for celestial gear provide a lot quality of life. Another area where celestial gear/builds shine(s) is WvW (roaming).

And even in so-called endgame content, e. g. Raids, (CM) Strike Missions and (CM) Tier 4 Fractals, I would suggest to find other people to play with, if your group complains about you running a celestial build. Assuming of course that your build is suited for celestial gear and you know what your are doing.

Always keep in mind that your are doing no damage, no healing and do not provide boons while you are dead.