Stop default application per file type changing I'm now on High Sierra but have had this problem previously on El Capitan.

Sometimes, even directly after a reboot, files like .png or .jpg open, instead of in Preview, which is what I want, in some ancient canon photo util programs I still have on my system (which I should probably delete).

I'd like to know what could be happening here and to investigate - can anyone advise how to precisely control filetype associations and what are the common causes of this getting messed up?

Following other questions on this topic, if I do:

cat  ~/Library/Preferences/com.apple.LaunchServices.plist   

I just get:

bplist00?

Then if I view this file in vim, I get some unreadable characters. It turns out (after a quick search for bplist), that this is a binary format, so not editable in a text editor.  Is my only option to delete it?  Will it be regenerated?  Is there a way to view what all associations are currently and pinpoint all sources which may change them? Thanks.
A bplist is likely a "binary plist" file, which is why you see junk when you open that file in vim. Try opening the file with either something like BBEdit or if you have the developer tools installed, there should be a command line program called plutil that you can use to convert to and from a binary plist.