In my company, the policy is that a non precision approach can be flown using a profile which puts the aircraft lower that the notional 3 degree glide path should the weather conditions suggest you are going to get the visual references late. This allows a level off at MDA (M meaning Minimum and therefore no go below), and continued level flight to the MAP at the approach minimum. If you aim to level off at MDA from a 3 degree path, by the time you have levelled off, you are going to above above the optimum approach angle and may have to go around. This only works with MAPs which co-incide with the 3 degree path, which most do these days, particularly if coupled with DME.
Descending to MDA from the FAF providing you don't exceed RoD limits (which are generous) is allowed, providing you stay in the approach lane. The only exception to this is the SRA where the MDA is calculated using the notional 3 degrees to lower the minima.
DA is the altitude where the decision is to be made. It allows for look up time, time to decide, time for spool-up and time for the aircraft to overcome the inertia of the descent and actually start climbing.
MDA if used wisely can be used to your advantage. Adding extra for dip is adding an extra limitaion and more constraints IMHO.