On the B747-400 our procedure is to push the thrust levers up to about 70% to ensure that all the engines spool up together. Then we push the TOGA button.
If we are below 50 knots and the flaps are out of up (which they need to be for take off) pushing the TOGA switch activates the autothrottle in THR REF mode at reference thrust limit selected on THRUST LIMIT page (on preflight) and displayed on the upper EICAS.
It also updates the FMC position to runway landing threshold if the GPS updating is not active.
However, if we push the TOGA switch after 50 knots and below 400 altitude the autothrottle will not activate!! I'm sure you can work out what that does for the workload on the runway.
I hope that helps