That’s a clever advice, in tagging approach ! I never realised that. 
I’ve always used the Scan button because I have always merely used Picard as a PUID/AcoustID submission tool (unfortunately, though, I have to rip for that so I tend to submit fewer stuff nowadays, no time to rip).
Besides that, the Scan button can also be useful if you have a 02 - Track 02.wav file and you don’t know what it is. Sometimes, if someone has submitted its fingerprint, you could find the artist and work name. Such a cool stuff ! It happened to me once or twice or more, and I was so grateful. 
This is why, even if I submit them less and less because of necessary ripping, I still do it for stuff I really like in music, so to people could find those I recommend, at least. Strange behaviour, isn’t it ? 