Well a drill or an "E-file" as people refer to it now a days, is just what it sounds like ... ie an instrument that has a bit which spins at varying levels of RPM's. These bits come in many variations for doing different jobs ... sanding disks for filing, buffing bits for creating shine, cleaning under the free edge etc etc.
NO ONE should make a purchase without ensuring they have a thorough education on how to use this implement safely, for as one can imagine, it is possible to do allot of damage and cause allot of pain if used incorrectly!!
Why do technicians chose to use them? Some technicians believe it is quicker than hand filing to use an E-file. I think it depends on the quality of the work as to whether or not it is quicker ... If one does perfect work with their brush and creates beautiful thin nail enhancements there is no need to use an e-file ... but it can be quicker if the nails are thick.
Remember that e-files create much more dust and finer dust which stays in the air for a long period of time. Best to wear a mask when using this instrument.
