Register as a ltd business ?

Hi

I am in the process of writing my first app, only I'm not sure if it would ever make a lot of money maybe a few k if I was very lucky

my question is should you register yourself as a business (limited company) before you start selling software ?

what kind of protection can/ do you get if you don't (from someone suing you) ?

the thing is it seems a lot of hassle setting up a ltd company just to brake even !

thanks

Stef