No, but they do expect you to vacuum in dark areas of a room, such as corners, under furniture, etc.
I actually asked a sales man this question once and his answer seemed resonable. He said that light is for areas of your room that have low lightshadows and such. For example, behind a couch or under tables. I never vacuum those areas so I had no idea. It is helpful once I put it to the test. The light needs to be a little brighter on my Kenmore. My Dyson (newer one) does not have a light....I dont think.
So oncoming vacuums can see them coming easier. Seriously, it's probably so when you're vacuuming under or behind something where it is darker than the rest of the room, you'll be able to see and also if you come up on something small that you might not normally see without the light, you may be able to avoid vacuuming it up.
It makes it easier to see things that you maybe are not supposed to suck up, for example pins or thread that can hurt your vacuum.
for the reason above and some places you vacuum you might not ber able to see well, as in corners around furniture, or under coffee tables and such
