It is a neutral thing. Just one part of their strategy.

In the old world, the majors owned (or leased) all the airframes and found a staffing agency to crew them. The only exception to that model is SKYW airlines. SKYW owns (or leases) almost all airframes. There are a handful that are DL owned.

That provides more leverage for SKYW to negotiate with cash strapped majors and provides more stability to the employees as it is much harder to whipsaw.

Everyone else pretty much staffs aircraft that are owned by AA, DL or UA.