If you're having a male cat neutered, then it probably won't need any stitches. If your cat normally spends a lot of time outdoors, then you might think it's OK to let it out once you get it home. After all, you won't have stitches to worry about.
However, you should keep your cat indoors for a few days anyway. Why?
Your Cat Might Not Be Sterile Yet
When your cat is desexed, your vet removes its testicles. This makes the cat sterile. It loses the ability to produce sperm. However, you don't know if your cat has any sperm left in its tubes from before the operation at this stage. It might not be sterile immediately even though it no longer has any testicles. This only happens once any residual sperm dies away.
This may be a small risk, but it is still a risk. If your cat recovers quickly from the operation, then it will get its energy back quickly. It might feel quite frisky. If it meets a female cat, it might even be able to get her pregnant.
So, it's a good idea to keep your cat indoors for a few days. This ensures that it can't accidentally father any kittens.
Your Cat Might Be a Bit Vulnerable
After desexing surgery, your pet needs to recover from its anaesthesia. While it won't have stitches, there will be an incision line that needs to heal on the testicle sac. In some cases, your cat may need to wear a protective collar for a day or two. This prevents it from licking or chewing at the incision line so that it can heal without the risk of infection.
Even if your cat is fit and healthy, it shouldn't roam around outside while it's wearing a collar. The collar impedes your cat's peripheral vision. So, for example, if it climbs on a fence or up a tree, it might fall and hurt itself.
The collar itself poses a risk. If it gets caught on something, then it could strangle the cat. It's safer to keep your pet indoors until the collar comes off. Even if your pet doesn't have to wear a collar, it's wise to keep it safely inside for a while. You don't want it to get its incision site dirty or to accidentally pull it open as it roams around.
To find out exactly how long your cat should stay indoors after pet desexing, ask your vet for advice.