Is it best to install security lights on their own switch, or not?

I am having security lights- with a motion detector that trips the light for 20 seconds- installed on the outside of my home. Should I get the electrician to install them on a switch that I can turn on and off? Is there any reason I wouldn't put them on a switch, (it does cost more to wire that way). I just don't want to have to get it done later if it is best for them to be on a switch.