The dual throttle up is not done by every airline and is not recommended on every aircraft, especially boeings where the throttles move themselves in response to things like TOGA.
N. Molson is correct is what he says though.
Safety. You NEVER take your hand from the throttle during lift-off and this applies to both pilots.
Not quite true. The normal SOP for most airlines during take off is as follows:
1. Throttle up to 60% N1, wait for the engines to stabilise
2. TOGA. PF or both hold the throttles at TOGA power
3. PNF calls '80 kts'. PF calls 'Cross checked' - this confirms that both Speed indicators are matched.
4. PNF calls 'V1' - PF removes hand from throttles.
5. PNF calls 'Rotate' and PF lifts off
6. PNF calls 'postitive rate' (Aircraft is climbing)
7. PF calls for the gear up.