I actually use the back button during the raid events. When I use gacha and collect the items (like from PP) and get a stack of tickets. I click back button to go back to the event gacha page faster to use them. It really depends on how deep the page is and how many clicks of navigation it takes to get back there.

The most useless one I feel would be the Raid Invite auto popup window. All it does it slow you down. Sometimes it can cost you the whole raid if you join when the HP is low. If I wanted to invite, I could just open it myself. :/

Daily Free Gacha is very useless too. Even to new accounts.