lps and softies go well together. lps and sps is a whole different ball game. LPS -tends- to have a better defense mechanism than sps (in my experience) and will destroy a colony of sps quite quickly once it is discovered. Basically it's best to have things separated as well as possible.
Secondly, sps needs really really 'clean' water to thrive, and lps does fine in fairly dirty water. For example in my tank I have to spot feed the lps manually or they don't grow at all. I spot feed the sps too, but a totally different food, and food+food can lead to a host of different problems (I can get algae buildup on the substrate when I've been feeding, but the corals will look great)