I was a poll watcher in high school-- you didn’t have to be a registered voter then. One thing we were watching for was volume. At the time, the voting machines didn’t record the time people voted, and the poll watchers records were the only record of when the polls were crowded, and when they were empty-- also, and we weren’t supposed to let on, but because it was a primary, we were listening to whether people asked for a Republican of Democrat ballot, mostly to get an idea of whether the parties tended to vote on different timelines (they did-- Republicans voted first thing in the morning; Dems voted at lunchtime, and after work). The information was used by the party I worked for to advise people who asked when to go to the polls to avoid crowds, and also to know to ignore early reports made by interviewing voters at the polls that Rep candidates were in the lead. We also used it to help volunteers who drove elderly people to the polls-- people who happened to own vans, which was less common then, would volunteer to go to retirement homes, and drive people to their voting place. Retired people were often free to go at just about any time, and information from poll watchers helped determine when infirm people would do the least amount of waiting.
We also did some trouble-shooting. This was before cell phones, and sometimes when there was a question one of the poll workers needed to make to the city registry, but weren’t allowed to leave the polling place, and there was no phone in the polling place, we’d go relay a message.
We were general gofers too. We’d run to the teachers’ lounge and buy sodas for the poll workers. We couldn’t sit in for the certified poll workers, but we could sit in for the pollbook holders if they needed a bathroom break, and we did that. When the lunch cart arrived, we helped them unload.
We also did a little crowd control if it was necessary, after the polls were closed. Since the workers couldn’t leave the polling place, we stood outside and informed people who showed up after closing that they were too late. I only had to do that twice, and only go back-talk once.
If we had observed anything untoward, we would have called the precinct committeeman, but I personally never did. I did see one inspector who was clearly incompetent, and reported that, but so did three of the poll workers, who were not happy about being kept at the polls unto 1am (typical was 8:30pm after a close of 6pm), because the inspector had no idea what was going on.