Yeah, 10 more seconds is at least, if not more, than double the ACTUAL time it would take off the clock. We're talking 3rd and long here, with the defense knowing what you're going to do. Can you break one for the first every now and again? Sure, we did it this week. Is it more likely you're going to get stoned at the line and burn maybe 5 or 6 seconds off the clock? MUCH MORE LIKELY. Of course, you can take the middle ground, a short gain, burning 8 or 9 total seconds off the clock. That's as opposed to burning about 3 seconds with a kneel-down play--oh, yeah, you know, QBs don't always just dive-to-the-ground kneel as quickly as possible--it does happen sometimes that they drop back a few steps and then kneel.
And if you're in 3rd and 13, the odds of you having to punt anyway are astronomically high, when you're running the ball, and the defense knows it. So you give up maybe 5 seconds...which might--MIGHT--be one play, while guaranteeing you aren't going to fumble. Sound logic to me.