The sad thing is, sods law, whilst having a good chit chat at the bar on say a380 biz and doing about couples bottles of nice wine, or heck even in cattle in the area in front of emergency exits on wide bodies with fellow passenger consuming a few cans of beer (not sure if that works in US - definitely fine on Emirates, SG, Qatar and Etihad) pretending to stretch legs for a good hour, if there is any turbulence I'm probably going land on this guy's head, if he got up and moved about he probably would of survived. Not sure how you quantify that risk. Again, realistically, it so remotely low that any inconvenience isn't worth considering. Partially joking here, partially not.... Just ridiculous to worry about this remote chance to point of strapping yourself in for 10hrs+ and not moving

There are simple exercises that you can do while seated to avoid DVT. Just wriggling your toes help a lot, or flexing the muscles in your legs.

I fly a lot on routes over the tropics and have experienced serious turbulence multiple times. There's no way I will be wandering around the cabin unnecessarily.