I believe anything quicker than a 10.00 requires a closed face helmet (check the NHRA rule book). Other than that it's personal preference and how comfortable you are with your face being exposed. I prefer it for visibility reasons.
You are correct, thank you."any car running 14.00 and quicker in the 1/4 mile requires a Snell 2005 or newer OR SFI 41.1A helmet (see complete list below)". Also a new NHRA rule in 2008 requires that "any car running 9.99 or quicker in the 1/4 mile requires an NHRA approved FULL face helmet with visor.