I've used -3db gain 99.9% of the time on every camera I've owned in the past 20 years except one. That inlcudes Ikegami betacams, Ikegami DVCAMs, Z1U, EX1, EX3, F350, etc.
There's no question that -3db reduces noise in the blacks on those cameras. However, according to some people it also may have reduce the dynamic range. But I don't know if that is true or not. If it is, then the difference is extremely small, and the trade off of cleaner blacks is well worth it.
The one camera that I do not shoot at -3db is my F800. The blacks are so clean that it is completely unnecessary. So, on the slim chance that I will lose some dymanic range, I don't use it. I only drop down to -3db for times when I want to open the lens a little and changing the ND filter would be over kill.