I had to think of this statement - and thought I’d like to say the following:
While I am rather a lazy guy, I went ok with learning the guitar (I like to think this at least 
) I often tried to combine useful things and spend my time with either fun or really useful stuff and Justin sounds the same in his lessons. While he says he was crazy practicing scales and hard excercises in younger years and it was kind of fun for him, so ok, he wouldn’t give this as a recommendation.
So, I’d rather recommend learning the more important, or say more often used keys (well, I mean the chords in those keys) than ALL of them. Or at least start there. Like certainly, C, G, and then… D, A, or E? I’m not sure, but I think a good way would be to attach that to a song you like and you learn anyway at the moment. See the key it’s in, which Chords are used and think where in the key these chords are. Like Cherry Wine (when ignoring the Capo) using a G (I chord) then C (IV), then Em (vi) for example. And explore the other chords in the key that the songwriter left out.
Concerning chords and their function/relation, I liked this video : Video about Chord functions and relationships
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Sorry for talking so much on your learning log! I hope there’s some bit that makes sense somehow
Ah, yes, this reminded me why I was never so much a fan of blues in general (with lots of exceptions! - we talked about it before) … I think oftentimes it somehow sounds similar to what Brian posted here in the comedy thread Just a couple of Music related funnies! - #521 by brianlarsen