I worked on GM black box and technology / information integration probably over 10 yrs ago. I'm sure they're more sophisticated now. Back then we collected about dozen data points and relayed them real time through OnStar to GM data warehouse. So if engine light comes on, GM would know about your issues. Where they were going with this, is if engine light comes on, they were going to mandate that you bring car in for servicing within so many miles or the would void your warranty. Ie they didn't want people driving for miles with something wrong until smoke comes from the engine. Obviously we ran into privacy issues etc. So now GM collects this data passively and they perform analysis on driving, car troubles, quality assurance, etc. In case of accident the data points are available and can be used for insurance purposes. If you know about this 
