I know some servos are not rated at 6v, so a regulator is needed. I've used the Mini Hobby regulator with good luck, just make sure you plug it between the RX and Switch. If you plug it between the BAT and Switch, it will drain your pack.

That being said, I know guys using straight 6v packs without regulators and they seem to have no problems. I just started not using a regulator with my 6v pack and so far so good.

JR Gautreaux