I've been discussing backgrounds with other cartoonists, and I thought I would share my observations with people that maybe care for that sort of thing.
For many it can be a pain to have to think of what to put in all that dang negative space. I totally used to over do backgrounds, unnecessarily. Your backgrounds should have a purpose. Generally they are used to set the atmosphere. You see these a lot in the comic's establishing panels. How to use panels are important, but also what you use for backgrounds is important.
When it comes to backgrounds, for me it helps to really know where my characters are. I know their flats and neighbourhoods in my mind to small details. For me the environment they live in is as much a character as the characters themselves.
We have Kukträsk, the cold, sparse town in the polar circle. The very absence of a detailed background can say a lot about where they are.
Does your character live in a student flat? Perhaps she really values a nice looking home but doesn't have a high budget and absolutely refuses Ikea.
Or perhaps she really, REALLY loves the complete Ikea package. (She totally gets bowls of chips and cider out for Eurovision Song Contest, all dancing on her sofa. Cries herself to sleep after.)
Or do they live in a warm, old part of a large European city.
All that said, I sometimes totally skimp out on backgrounds due to time restraints. I generally use photo references but sometimes I just go from memory.
