The satfile is a file inside a receivers software that has a list with satellites and the transponders for each one.
The receiver has to have it to get the channels from the satellite. The providers often change transponders so you always want a updated satfile.
Now SOME receivers can do what is called blind scan and do not need a updated satfile.
Just a note here lately we have seen with the viewsats and others that during the update process sometimes information from the satfile is getting corrupted. That is why we suggest users always install a fresh. updated copy of te satfile every time they update a receiver with a new bin.
Hope that clears that up if you have any questions please ask