A couple of months ago, I learned a tough lesson about combo draws on a $1\$2 risking $200. I picked up KK in the SB and popped to $20 and got a caller.
The flop had two suited connectors, and I bet the pot and got a call. The alarm bells were ringing.
Thinking he was on a nut-flush draw, I bet big on an innocuous turn card. The villain shoved and I was pot-committed and called. He hits one of his numerous outs on the river and stacked me for $200. Not a fun way to head into league night... :-(
I went back and analyzed the hand in Poker Stove, and it was eye-opening to see how behind I was on the flop even with a strong overpair, and that was my introduction to the power of combo draws.
Last Sunday, in the RTR Freeroll, I was in a hand where I hit an open-ended straight flush draw on the turn card, and I had already paired the board with a mid-pair. Coincidentally, I had lost some chips early on to the villain in the hand. I recognized an opportunity and fast-played the draw all-in. The villain hit two pair on the turn so he was committed and made the call.
Fortunately I hit one of my numerous outs and stacked him, then went on to take down the tourney for $200.
Here is an article that explains how powerful a combo draw is.