Fyi, they've done studies on the subject and the answer is "no", it does not significantly improve efficiency. It's main purpose seems to be to more easily keep your feet solidly connected to the pedal - if you were spinning at 120rpm while racing, your foot coming off the pedal would be a disaster.

There has been a lot of debate on whether clipless has no efficiency improvement, or a little, and I don't care to wage into that, but I wish I had known that the difference was small at best before going through all the hassle of different shoes, fittings, etc.

Fyi, you can buy bikes shoes that are designed for biking but without the "clipless" part. Here's one example from Specialized, a lot of other brands sell them as well:
Specialized Bicycle Components

You can combine them with a good platform pedal with pins (again, this is the Specialized version, other brands make their own as well):
Specialized Bicycle Components

And get most of the same grip as with clipless that's a lot easier to use for commuting than clipless - or straps or hooks or anything else - is.