Is it worse to use _global or lots of _parents?

So I have a huge project which involves lots of movie clips calling to eachother, is it better to set globals and call to those or do _parent._parent._parent ( sometimes up to 4 _parents? )

  1. Will I run into any conflicts? I know _root. is BAD because of externally loaded swfs and such.

  2. Will it take more or less memory / cpu power perhaps?

  3. Is there any disadvantages to using _global besides it REALLY needs a unique name?

Thanks!