I find 0.5 and 0.7 pretty interchangable for what I do with them. By choice, though, I use a lead holder, and swap out leads depending on what I am working on.

Now, technical pens? Yeah, it matters a lot for me to have the right tip for the right job. And they stopped making technical pens, so I'm very careful with them.

Mind you, I can't find my damn ink!