Turbo Trainer Advice

do you use it powered or not?
Usually powered, but have used it not plugged in and makes no difference. I plug it in because I worry about overheating without it’s internal fan running, but have no idea if this is really necessary.

is there a bit of 'wobble' built into the design? i.e like using a rocker plate?
Yes, it sways a bit side to side. It definitely helps with comfort during long sessions.

what is the significance of the light that it emits on the ground?
It changes colour depending on intensity. Blue for steady, purple for tempo, red for threshold (I think). Serves no purpose obviously, but looks futuristic if that’s important to you.

Yes there is a bit of wobble, but not to the extent of a rocker plate.
Maybe similar to the rubber feet on the latest gen Kickrs?

I use mine powered, because I can, and it adds road surface emulation and downhill emulation, but irrelevant for structured workouts.
It was my choice as it can work unpowered for race warmups.

The light goes red when you’re working harder, and illuminates the puddles of sweat and tears.

There's quite a lot of wobble, which initally had me googling to see if there was something wrong with it, but now I'm used to it seems like a huge improvement over other trainers in terms of feeling marginally more like riding a real bike.

Powered is generally better just because it totally cuts out the moment you stop pedalling and there seemed a slight delay for sensors reconnecting, etc. PLus as others have said you miss ouyt on the totally pointless vibration effect, etc.

The lights have always seemed a bit generous in terms of sensitivity to how hard you're working - they go red on mine even when not working that hard.

Basically what everyone else has already said and I'm only replying here because I'm putting off doing an FTP test.