Ivan, they aren't really presets. More like Fisher suggestions for turn on and go use. The 1-10 markings on the various knobs (except discrimination) are all in gold except the Fisher "suggestion" numbers are in red.
Basically those are suggestions to be ignored. The sensitivity red number is 3. Most cz-3ds get max depth at 5 or thereabouts. Beyond that, you don't get more depth, just a wider coverage area and usually instability if you go much over 5. At 3 you lose a good deal of depth, and I would never use that setting unless EMI forced me to. The lowest I've ever had to go because of EMI was just slightly above 3.
The volume red mark is at 5, go lower and you'll get more modulation on the deep targets. Go higher and you get less.
Likewise the GB red mark is 5 and if you have average ground you should be pretty close. at 5. The mineralization in my area is moderate. I always GB and find I'm between 4 and 7, average around 6.
When the 3d gets a little chattery, Re-ground balancing sometimes clears that right up without a need to drop sensitivity.
The cz-3d is not one of those detectors where you "work into the noise" of EMI. You want it to run quiet to hear those deep soft hits.
The discrimination knob is at 4, but I never run the cz-3d at anything but 0. That is the optimum setting for determining the iron falses from the good targets.
Back to your original question. You probably wouldn't lose much performance if you have average ground by leaving the GB at the 5 red mark. But, as others have said, ground balancing is so easy and quick. There really isn't a logical reason not to.