I don't use a strap and if you do this for a while you'll press your forearm automatically with more pressure to the uke-body.
There a some songs where i change rapidly between super fast fingerpicking and strumming where a strap would make it a lot easier.
Next thing would be the performance question:
If you want to do more than just playing the ukulele on stage, a strap allows you to grab easily other things like another instrument or a mic.
The important thing is only that you play really good and the rest doesn't matte r (uke model, color, your outfit, a strap)