Do I need a good computer for aerospace engineering degree at Sheffield?

You won't be required or even expected to do any heavy duty technical work on your personal computing equipment. You'd be expected to use uni computing clusters - and since many of the programs you'd be using are extremely expensive to have a personal license for, it's not normally worth getting a personal license anyway (and the uni license usually won't allow you to install it on your personal machine).

Just take whatever fits your needs in terms of your personal usage - the main academic use for your personal computing equipment will be word processing things and doing research on the internet with it, and maybe some excel stuff for handling data.

Thanks for the advice, thats odd as it goes against most of what I heard from other forums that always suggest a good computer. Thats why I wanted to ask more uni specific answer. Any ideas of the typical programs/software used?

Probably stuff like autocad, solidworks, in later years FEA software. MATLAB is probably ubiquitous too. Maybe SPICE if you're doing electronics stuff? All of this stuff has really expensive licenses and is not generally worth getting a license for. All of them will also be things that area available on the uni PC clusters in the department, which will usually have been set up specifically for this kind of work too. Possibly also some general purpose programming and using some kind of IDE or something (although a lot of these are easy enough to set up and run on almost anything as long as the thing you're programming isn't super heavy duty), which is probably the exception.

The only stuff like that I did from my personal laptop when doing engineering were basic programming exercises (which could've been done on anything) and the major thing that might've been more involved wasn't even for a module on the programme itself, it was for a summer research project I did, and it was using an opensource software anyway (which granted, ran a lot faster on the uni PCs, but I COULD set up a model to run before I went to work for my part time job and it'd usually be done by the time I got back). Had I not done that, I could've certainly made it through with just basic office software for my personal computer and using the uni PC labs for anything else pretty much.

Just get whatever suits your needs - which might be a higher end one anyway, if for example you do a lot of PC gaming and need a good GPU. But don't bother with that stuff if it's not something you'd use for your own purposes.