axs In an abstract sense some system app may not really need some permission. Maybe Settings doesn't really need sensor access, for example. But the Settings code inherited from Google may "know" it has access to all sorts of things it doesn't really need, so it might blindly poke at some sensor. Because that has never failed before, there may well not be code for handling the failure gracefully (things that are not tested often don't work well).
So removing sensor access from Settings might cause it to crash -- maybe as soon as it's launched. And without a working Settings app it would be tricky to restore sensor access. People have "successfully" found ways to disable things that have resulted in no way out but a factory reset.
My suggestion: if it came with GrapheneOS, don't try to delete it or disable it or remove permissions from it before you've carefully read the source code for it and everything that will try to launch it. If finding or reading the code is infeasible, that may be a good point to stop. Just a suggestion!