lol - it heats up.

Some plastics stick better to a warm/hot bed and come off better once it's cooled.
Some plastics will only stick to a hot bed.

Some will work with either hot or cold.
Basically a heated bed increases the number of materials you can use and in an enclosed printer like the dremel would mean you could print fairly easily with things like abs and nylons which prefer not only a hot bed but a heated enclosure as well.

Abs pretty much won't stick unless it's a hot bed - although geoff has recently proved otherwise.

But basically it's a very useful thing to have.