Would two prime lenses with marginal differences in focal length provide the same level of versatility?

Example, a 30mm versus 35mm.

I'm going to pull the trigger on buying new prime lenses soon for portrait photography. I will likely start with a 50mm, but smaller focal lengths like the ones above - as well as larger ones like 85mm - are also part of the plan.

Speaking about prime lenses in general, not just the examples above, do small differences in focal length between two lenses have different use cases? Or would there be no difference?