I assume from your handle that you are a 747 pilot. If so, the answer is yes - it's a performance thing.
But also, if you are flying a 744 or a Classic with FFRAT and using the AT for take off, you should have set take off thrust by 65 Knts IAS. This is because the THR HLD funtion is activated and the thrust lever motors are declutched. If you reach 65 Knts IAS and you haven't set your TO EPR (N1 for GE engines), the AT obviously won't do it and you have to do it manually. If you haven't set it by 80 KIAS, you should really be thinking of setting GA thrust because by now your take off calculations are now compromised.