When I started driving I checked the blind spot pretty much all the time, I think it was because I rode a moped for a while before hand where it was essential - the "life saver".
Lately I've been doing it more again because there's been a few moments when getting on a certain motorway I've missed seeing cars already on the motorway. It's an odd one where my car has shit mirrors and the motorway is higher than the slip road.
EDITED: 1 Apr 2015 10:58 by ANT_THOMAS