I always had "flat" shaped tip until I discovered DrDave and other teachers so in order to further improve I switched to their proffered shape and was not happy at all thinking that I have to improve to benefit from it..
Recently Reyes had interview where I found out that he had his tips made almost flat as well. I flatten my tips and guess what? I can still draw good and once again I can control cueball way better.
I think that we all need to experiment and find what works best for us. Different cues, cue weights, tappers, tip sizes, cue balance, shaft kinds, stroke types affect how cue plays, only experimenting can help. I dont think there is general rules for this. I only think that soft tips let us control cueball better in short distances and play & control short positions easier.