User blog comment:KirbiMiroir/Classic Mode - Redone!/@comment-25275196-20160827111859/@comment-25275196-20160828080639

You choose what stage you want to play in the menu. Each time you win, you go up a level, and you can choose a different stage, or go straight into Crazy Hand. Damage also carries over. The more stages you can clear, the bigger the prize is, but you need to defeat Crazy Hand to collect it, otherwise you get nothing.

Basically, it's a temptation for a bigger reward that you may or may not get (think Deal or No Deal).