For a while when I was using non-heading-hold gyros, I moved Gyro sensitivity to channel 7 which uses a 3-position switch on the front of the transmitter. In the bottom position, the gyro is set to low gain for pirouettes and the like; in the top position, it's set to high gain for hovering; in the middle position, it activates a rudder-to-gyro programmable mix which allows for fast pirouettes and 540 - 900 - 1080+ stall turns.

I have also been using channel 8 to control the gyro gain. This is really handy when dialing in a new piezo for the first few flights, since you can tweak the gain quickly using the knob on the front of the transmitter.

The 8U transmitter includes a pair of dedicated 5-point mixers originally intended for control of a remote needle valve. The master 'channel' is the throttle stick position, the slave is channel 8, and there are separate curves for normal and idle-up flight modes. If you hook up your gyro gain to channel 8, you can have a high gain in hover, and a slightly reduced gain in idle up to keep it from wagging in fast forward flight. That makes for one less switch to flip while keeping the highest possible gain at all times, which appeals to me. For more detail, see this web page.

The 8U allows you to assign dual rate functions to different switches, so I put both aileron and elevator rates on the "A" switch (rather than A and D). This allows me to adjust the entire cyclic response at once, which suits the way I think of things. This also frees up the "D" switch for other things...

If you've given your helicopter a new engine, or new blades, you might be wondering how much pitch is appropriate. If you have a spare p-mix, you can set up something 'dual rates' for your collective. This lets you try two different pitch ranges in each of the flight modes, which I find helpful when evaluating pitch <-> RPM tradeoffs.

PMIX-2:
Channels: PIT -> PIT
Percentages: +20 / +20 (for starters, use more or less as you please)
Turn off all the mixing options; link off, etc
Assign the mix to switch D

When you're satisfied with a pitch range, it's probably best to either disable the mix and set the ATVs to give you the range you want, or set things up so that the 'low' rate is what you fly with 90% of the time and the 'high' rate is just extra pitch for drag racing or whatever.

In my opinion, flying around on 'high' rates is somewhere between a potential annoyance and a potential disaster. The other day I was wondering why my heli wasn't performing, and it turned out I had the collective on the 'low' rate... annoying. Had I starting doing low tumbles at the start of a flight, it might have been enough to cause a crash. On the other hand, if you normally use 'low' rates and accidentally hit 'high' rates, you'll be more reponsive and thus more able to recover from the surprise.

Your mileage may vary, but that's my take on things.