Generating Lightmaps in Unity vs Using your own UV's

Hey guys, I'm working on a game for iOS and I was wondering whether it would be better to layout my UV's myself (no overlapping) or letting unity layout my UV's for light mapping.

On one hand if I let unity generate them I can really pack my UV's and save on how many materials I have to use.

On the other though I'm worried that if I let unity generate a second set of UV's for light mapping I'm gonna have a bunch more sets of UV's

Just wondering which would be better.