Guild Wars 2

…but can’t do anything with the instant 80 boost. I hardly play my alts so won’t ever start a new character. Can I just destroy this useless thing and use the shared slot for something that’s actually useful?

You can use it on a level 80 character to get all the items that go with it

https://wiki.guildwars2.com/wiki/Level-80_Boost_Package

Why not just use it on an alt that’s not 80, even if you hardly play them? Or if they’re all 80, just make a random new character and boost it. Then you’ll have your empty slot.

You can claim it on a level 80 character as well, if I recall correctly. I’d still pick one of your alts to boost. You never know when it’ll come in handy to have an alt just stashed somewhere to pick something up once a day.

If you have any unused char slots then definitely create a new toon and boost it to 80. Then use it a storage toon (“mule”) for all the oddball account-bound stuff you have collected but will probably never use.

If you don’t have a spare slot then yes, you can boost an existing toon, even a lvl 80, or you can just discard the booster to get access to the shared slot. Mind you, you said you don’t really play any of your alts so a shared slot is not going to be that useful to you in any case.