I didn't watch the whole thing, but, please don't scale one island on your UV layout just to fill space like that. Yes there are times you can mix and match UV scaling, but that is NOT the time.

Also, the margins/padding he's leaving between the islands are concerningly small. You generally want a couple full pixels between islands, to avoid issues with mipmapping and texture bleed from one island to another. If you know your render engine well, and the exact end use of what you're making, you can sometimes have tighter margins, but the safe bet is a little more padding.

I realize he was just touching on those topics quickly, but I feel like it would have been better had he just pointed anyone interested to his UV'ing tutorial [I haven't watched that, but surely it addresses those concerns?] after the smart unwrap rather than throwing out potentially troublesome ideas.

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