"Global" imports vs scoped imports

[Jeremy DeHaan]

I am working on a library, and I put all imports at the top of my 
source files under the module declaration. I was starting to 
think that it might be a good idea to start scoping some imports 
to reduce the number that might be used by a giving project, but 
how beneficial is this? Are there any kind of general rules for 
when to use module level imports vs scoped imports?

Thanks!
      Jeremy