Getting up to release fuel
 

Under what circumstances would you go back to the gate to add 2000lbs of fuel to get you back to the release amount?
How is this different than getting a lower altitude assignment than requested and burning extra fuel doing so -- you'd still reach your destination with lesser than planned fuel on arrival. Why not continue the takeoff and ask for a re-release from dispatch while in flight.

For me it's when I will no longer have Trip + Alt + Final Res.

From actual dispatch, you have contingency fuel available to use. Going back to the gate should only be done if absolutely necessary. You can use contingency anytime from dispatch. Options then become inflight replanning. Can you specify a closer alternate? With good weather, can you lose your alternate altogether as you get close to destination if the destination has more than one runway?

There is a culture difference here- to European eyes, the US Dispatch system seems to give decision making to someone on the ground. Once the wheels start moving for us, total control and decision making is held by the flightcrew only, apart from company instructions- it's up to the flight crew to follow guidelines, as yours should be in the company manual