If you use inner tubes then if 1 foot gets caught you can't kick the other off. If you use the thick round heelstraps like many manufacturers make now then you can use the free foot to kick the other off which will save you a knee injury. Trust me on this one.
I have to agree with KiteKarl. It happened to me. On a wipeout,
one foot came out, the other didn't. The stuck foot came out of the
binding but ended up twisted aroind the tubing. There was nothing I could
do to get the darn thing off. Luckily, I got away with a mildly twisted
ankle and was able to kite the rest of the sesh.
If you're going to use a heel strap, get a thick one (like suggested above)
that won't be able to wrap around your foot and will be easier to
kick off. (I haven't used mine since... )