comma before 'in case'

[ademoglu]

Hi,

http://www.ldoceonline.com/dictionary/case_1

- Take an umbrella, in case it rains.

I would like to ask why the comma is used before 'in case.' Is it because of an afterthought or emphasis?

Thanks.

 

[MikeNewYork]

I would not use that comma.

 

[Rover_KE]

Neither would I.