[MD Longhorn]

10U - never. Never ever.
Ditto low-level 12U.

For anyone older, like Skaht... I ALWAYS pregame this, even with familiar partners. No one on, ball down the line or possibly right-center, I'll go out, expecting to come back in for run-down if necessary, but expecting partner to get all the bases on a single runner if no run-down.

From B or C, ALMOST never - on the rare occasion where there are 2 outs and the catch-no catch is more critical than the bases (like, last inning, tying run on).

All that said - it amounts to MAYBE twice a season. Exactly twice this season - once in 16U, once in high-school.

But the key has been mentioned above - PREGAME this. If partner knows what to expect, this will work out. If he doesn't, you could be in trouble. Plus - if you pregame the rare situations where you might go out, and partner is as described above (older, bad health, something like that), your partner will be able to tell you at that point, so you'll go out either far less likely or not at all. Conversely - a young partner who likes to run, maybe I go out slightly MORE often, if it's discussed pregame.