I've found that to not matter that much these days - unless your projects is hundreds of thousands (or maybe millions even) of LOC, full builds are instant on modern machines.
any sizeable rust or c++ project is gonna take a while to compile in my experience? I tend to break things off into libraries that are faster to compile. Some of my coworkers don't like it but they learn to deal (c++)
I've found that to not matter that much these days - unless your projects is hundreds of thousands (or maybe millions even) of LOC, full builds are instant on modern machines.