Why should I record in flv format?
Most streaming and recording applications currently allow you to record in MP4, FLV and sometimes also in raw formats or MKV/QuickTime Video. But simple flv files have a benefit that is often overseen. If your software crashes while you record your greatest footage of all time, the flv file that was written up to this point should still be usable.
If you ever encountered such a crash, for example after a nice 4+ hour stream, and then had the problem that your recorded video files would not load in any media player or editor, that was because you did not record in flv format.
In general the flv format is just a container, similar to mp4. So your final quality will not change if you choose flv over mp4. And if you happen to use a software that needs an mp4 file later, you can easily convert the container without having to re-encode the video, so there will be no quality loss either. You can use FFMpeg for that, with a simple commandline:
ffmpeg -i filename.flv -c copy -copyts filename.mp4
I use this trick to get the flv files into Sony Vegas for example. And to end this very short article, there is no downside that I know of, in using flv over mp4. As mentioned, no quality difference but better stability on crashes is a big plus.