I mean modularization beyond the good practice, as in "this module ideally belongs in this crate, but I'll move it to another instead, so it will get recompiled less often".
I mean the time it takes to release a fix to production. It doesn't imply the production code is bad or untested. The world changes around code, so there always may be need to react, e.g. a 3rd party API may be down and I may need to switch it to another ASAP. Or my site may be getting spammed and I'll need to add tighter limits.
If I can build code quickly, I can rely on being able to be agile with the code itself, which to me is easiest and most flexible solution. But if I can't build the code quickly, I have to put more effort in ahead-of-time prevention, develop other ways of making changes quickly. This means that build time has a ripple effect that affects designs and development costs.