Can we disable main display ?

[Taisto]

As in the topic - i`m using full hd external monitor on my laptop with 10.5.6 and i wonder if i can use only the external display ? I have the options to mirror displays, to extend, to use external as main desktop but i`m concerned if there`s a way to disable the main laptop dispal completely and leave it running only on external one ? I think this would speed up my system a little ( or it woudlnt maybe ? )