You may not NEED your pinky toe, but it's incredibly useful and losing it can seriously fuck with your ability to walk. Your pinky toes help distribute your weight and it forms part of the "perimeter sensory system" in your feet that help tell your brain where your feet are and what's around them without having to look at them. Losing a pinky toe at an older age after you've already learned to walk can seriously fuck that up and negatively impact your ability to walk.
Now with Louie, given his sedentary lifestyle and massive girth, not to mention his fucked up ankles, likely already had a bad time trying to walk so might not have noticed as much when his pinky toe was amputated. However, he has mentioned a few times since having it removed that he's been falling over. Could be the loss of the toe. Could be his fucked up ankles. Could be just lol fat. Could be he was lying to gain sympathy for grifting.