Hi, had a few UMs and if you turn on the RX without the TX being powered the plane sits there flashing away waiting to bind, however you shouldnt need to do a rebind, if you turn on the TX the RX will usually find it and will just operate normally.
On the original point of TX RX switching routines - yes the Spektrum system safeguards against the accidental start up issue ( I use Spektrum on all of my planes) but personally I agree with the concensus - Power up the TX before the RX on start up and power down the RX before powering down the TX at the end of the flight.
A slightly different issue but one you need to be VERY
I was setting up an old plane on a new TX that I had only just acquired, the control surfaces were responding incorrectly so I went into the servo reversing setup on the TX. Purely as a result of being unfamiliar with the TX I scrolled one step too far in the menu and by accident reversed the throttle channel which of course resulted in WOT!
Fortunately it only cost me a new prop and no fingers!