I don't know if it is a huge issue but it is definitely a nice to have. There are a few examples I can think of:

1. I open the code in my IDE but build somewhere sandboxed. It would be nice if my IDE didn't execute the code and can still do complete analysis of the project. This could also be relevant when reviewing code. Often for big changes I will pull it locally so that I can use my IDE navigation to browse it. But I don't want to run the change until I finish my review as there may be something dangerous there.
2. I am working on a WebAssembly project. The code will never run on my host machine, only in a browser sandbox.
3. I want to do analysis on Rust projects like linting, binary size analysis. I don't want to actually run the code and want it to be secure.
4. I want to offer a remote builder service.

I'm sure there are more. For me personally it isn't a huge priority or concern but I would definitely appreciate it. If people are surprised that building a project can compromise their machine than they will likely build things assuming that it won't. Sure, in an ideal world everyone would do their research but in general the safer things are the better.