It's a question of probability math, taking into account how many rubies you have and how many emptying a pipe takes, and taking into account if there's spotlights or not (and how badly you want a specífic spotlight).

For example, this special pipe has 3 HE's, no spotlights, and takes 5 ten-pulls to empty. Each ten-pull has 0.6 (3/5) HE's on average.

If you get 1 HE the first ten-pull, you've beaten the average already and should reset if you want to keep pulling. After all, without a reset you'd be left with 4 ten-pulls and 2 HE's, which means that for the remainder you'd be down to 0.5 HE's per average 10-pull. The quality of the HE's is a constant here as there aren't any spotlights.

On the contrary, if a ten-pull yields less than the average amount of HE's, a reset makes no sense. For example, you've had 3 ten-pulls without HE's, so now the 3 HE's get divided by only 2 ten-pulls left, meaning if you keep pulling you have an average of 1.5 HE's per 10-pull. Much better than the initial 0.6 HE's that a reset would send you back to.

But the logic might change on pipes that have spotlights. Let's say a 50 pipe has 3 HE spotlights. Let's say only one of those you really want and need. If the first ten-pull yields 2 spotlight HE's, but they aren't the spotlight you wanted most, it's time to check your ruby count. Statistically, a reset makes sense as that would increase the average HE per ten-pull that way . But a reset would lower your chances of bagging that 1 really desirable spotlight from 1/40 to 1/50.

If in this example you're still left with enough rubies to empty a reset pipe entirely, the reset is the recommended play. If you have less than 225 rubies left (or 450 if we're talking 100 pipes), you might want to skip the reset in order to not risk missing out of your ultimate target.