perpetual - So they don’t have to set up some sort of content expiration scheme.
nonexclusive - so you can post it elsewhere and potentially sell it. If anyone asks for exclusive access be very very sure you are getting paid.
transferable - If they get bought by another company they don’t have to wipe all content.
royalty-free - They are not paying you to use their service to host your content
sublicensable - so they can have a 3rd party (like Amazon EC2) do the actual hosting, or provide another service with that content, like chat bots, giphy, etc.
worldwide license - They don’t have to geolock it
to use - Blanket right to use in their app
to host - Otherwise everything has to be externally linked
reproduce, publish, translate, distribute, perform, and display - Every time someone views the content it is being reproduced because that is the nature of the web.
modify, adapt, create derivative works from - Resize, transcode, change formatting, make thumbnails, etc.
in connection with operating and providing the Service. - Limits these abilities for the sole purposes of being used in the app. Excludes their use in advertising, selling their own copy of stuff, or claiming any sort of ownership outside of the Discord app.
I hope that helps. Legalese can be a little bit daunting but if you know what to look for, like nonexclusive and “ in connection with operating and providing the Service“ you can put your concerns to rest.