Thursday afternoon, you check Saturday's confirmations. Three people confirmed. Two haven't responded yet. You text those two. One confirms right away. The other says they can't work, but it's Thursday. You have two days to find someone. You post in the group chat, call a couple people, get it covered. Without confirmation tracking, you find out Saturday when they don't show up.
People don't check it
You posted the schedule on the wall, in the group chat, or in a shared doc. Some people checked it Monday. Some haven't looked since. They don't know they're working Saturday. You can't assume they know.
Smarteaming