Lesson BOO003 - Boor's Tusk

Late in the lesson, a few moves before the end, the lesson says that you should move rook to f1, while it discourages castling, which achieves the same, while moving the king away from the middle of back rank. Any ideas why is that so?

So this is in the course Slay The Slav With The Boor Attack.  Decidedly no expert here, but if you castle the K ends up on a dark square and can easily be checked.  The lesson seems to be all about keeping the initiative, and allowing your opponent to develop with tempo by giving a check is contrary to that idea.  You'll still be able to castle queenside.  I hope someone else weighs in on this, but that's my best guesstimate. 

Ah, yes, I see it could be checked, and initiative lost with next move than. Thanks.