In TvZ videos from day9 I saw the following a few times: Terran scouted Zerg base and scouted some spine crawlers. But doesn't try to go inside of the base, instead sitting outside and waiting. He scouts zerglings, banelings and actually doesn't move his hellions away but wait just where the creep ends.
From my perspective, Zerg can easily surround those hellions with some zerlings and kill them. Terran should constantly keep an eye on these hellions to pull them back and micro to keep them alive.
I don't think even PRO players constantly watching the mini-map. They need do other stuff and they risk to loose those hellions.
Question: What is a proper way to keep scouts on the front of opponent base and watch them constantly?