It depends on where you are and what kind of grass you have to a large degree. Where I am it's really difficult to mulch during peak growth in the spring and again in the summer if you have lawns with a lot of lush crab grass. I've run the mulch kits on both my 48 inch Turf Tracer HP and my 52 inch Lazer Z HP. However, I haven't run them in years. It's just too low going and too much of a problem if the grass is wet and/or you have lush lawns that get tall between mowings or if you're trying to tame overgrown lawns.
Personally I discharge most of the time and only bag if I really have to.
Now if you're mowing only well maintained lawns that are all cut every week and you don't cut in wet conditions, then mulching is a really nice option. I love not having to worry about where the clipping are going and my machines cut really nicely with the mulch kit on...like beautifully.