You don't need that pitch range for normal flight. I would suggest maybe setting at least -4 degrees in case the autopilot needs to make the heli come down in a strong wind gust with the main rotor in ETL. In Stabilize you can set your collective pitch range with the IM_STAB_COL params to limit the maximum negative pitch too.
For beginners who tend to panic by pulling the collective to the bottom when things go bad, you could limit the pitch to zero in Stabilize for learning so it doesn't slam the heli on the ground quite so severe in the panic 'pull the collective lever back'.
It is nice to have a bit of negative collective available in sport or scale type manual flying, however. For example, in the instance you have strong wind and have just landed, and want to "plant" the heli good before spooling down so it doesn't get caught by a wind gust and tipped over.