Warning! The following post contains spoilers from chapter 283 of My Hero Academia. You have been warned.
We finally get to see the side effects of Tomura Shigaraki’s incomplete surgery. Even with the impressive augmentations his surgery gave him, Shigaraki’s body cannot fully withstand the immense power the All For One quirk accumulated. Although he still can regenerate, Shigaraki’s healing process has slowed down. Despite his initial confusion, Shigaraki shrugged off this inconvenience and continued his assault on the superheroes.
The fact that Shigaraki cannot fully withstand his new power is similar to how Izuku Midoriya initially could not withstand the power of One For All after receiving it. One could argue that Shigaraki’s surgery was his equivalent to the hellish workout Izuku received from All Might before receiving One For All. This is a beautiful example of parallelism that further connects Izuku with Shigaraki. I suspect that even though he had his surgery, Shigaraki still has a long way to go before he is the ultimate supervillain and will have to learn to control All For One on his own. Considering the fact that Shigaraki is a fast learner, I can imagine he can overcome this limitation rather quickly.
If Shigaraki was able to cause this much damage at 75% completion, I can only imagine how much stronger he would be at 100%. That missing 25% was probably what would have allowed Shigaraki to master All For One through the surgery. Now, Shigaraki may need to acquire that missing 25% on his own with practice and willpower. I imagine that once Shigaraki truly masters All For One, he will be an even more overpowered monster than he is now. Only time will tell.