You then get Lefou back to your hand and can exert Madam Mim to play Lefou again, ready her again, challenge again, etc
Heres why players love it: 1
Red can easily generate mana advantage as well, be it through bursty rituals (Irencrag Feat), treasure tokens (Dockside Extortionist), free spell/polymorph effects (Fires of Invention, Tibalts Trickery), or the occasional outright mana dork/discounter/mana multiplier (Leyline Tyrant, Mana Echoes)
How many had a beer accidentally spilled on them or were drawn on by an unsuspecting kid
When any Dragon you control attacks, you get to draw a card for each attacking Dragon and then put a permanent card from your hand into play
Giving the controller of this spell full control over which permanents remain makes this significantly better than the average Wrath of God variant