They have fewer claws to sharpen on your furniture? 
I know a three-legged cat named Tribecker. IIRC, his front leg was very badly damaged while he was feral, and he had it amputated right away when he was trapped. He has this funny kangaroo-bounce he does when he runs. Sweet guy.
Awww. 
I saw a cat missing a hind leg jump to the top of our 6 foot fence, easy as pie.
You may be pleasantly surprised- Keyser was a real roamer around the neighbourhood- the neighbours would see these large copper eyes looking through a window or door. (At night but he used to get around a great deal during the day). However after the operation I think he seemed to accept he wasn’t going to be allowed to roam as much (he used to be a door dasher at first). He was happy to sleep in his yard and stay within the confines- maybe being an older cat helped. It was rather difficult when we used to get a cloud of corellas in the backyard (large white cockatoos) and he was isolated up the back but he’d just lower his head and charge through them and come inside.
They don’t have to lift their leg to pee? Oh, wait that’s dogs!
Seriously though, animals are amazingly resilient. I’ve seen shows where animals missing a leg function better without and prefer not to have a prosthetic replacement.
Also, unlike humans, domesticated animals don’t judge their house/yardmates by how they look.
Thanks again for all the support. I’ve decided to go ahead with the op and D (for Dood) day is tomorrow.
I’ve set up a Go Fund Me as the cost is rather horrendous. I have mod permission to post it here so here’s thelink. I will also be starting a thread. Note there is an update and plenty of pictures to make up for the bad link above.