Translation:The backpack is open, you are going to drop everything!
Depending on the style, some people might find them inappropriate. They're very common, though, and most people don't care much about them.
So it's basically as in English: they're ungrammatical, very common, and editors may complain about them - at least in formal writing. The rule isn't really taught in school, though, so there are a lot more people reacting to them in English than in Swedish.
I'm aware that we feature a few more comma splices than I'd like in the Swedish course, but considering that the system tends to screw up punctuation besides commas and periods, I think it might be better to leave them in.