Your unsaved edits are saved periodically in the background to a temporary recovery file. This saving process is very fast and you will usually not notice that anything is being done. You will not be interrupted. Note that Source Insight does use an automatic-save style of protection, because the recovery file is much more efficient.
The recovery file actually only contains pointers to other files. Therefore, it is small and fast to write out. By saving edits incrementally to the recovery file, Source Insight insures you against a system failure, power outage, or crashes. Source Insight will recognize when a recovery needs to be done the next time you run it.
You can set how often the recovery file is saved in the Options > Preferences: General dialog. The default value is every 15 seconds. If you make the recovery time smaller, the recovery file is updated more often. If you make it too long, you will be able to do many changes to your files without the changes being recorded in the recovery file. The recovery save process is usually quick, so you should the keep the period as short as possible.