For the most part this is easy to do and makes little difference. However there are some very minor negatives. First, the extra aeration from the spillover can sometimes cause the PH to go up constantly, and second the water diverted to the spa could potentially (but not likely) cause there to be too little flow to get proper circulation in the pool.
Of course "breaks up the surface tension of the pool" really doesn't serve any purpose, though it is often nice to look at.
Generally you want to spillover to run for about one hour a day, to insure the water in the spa gets properly circulated.
