If you add and/or are editing a booking in your Floorplan or Diary page, and it affects a rule within your Collins set up, a warning will pop up on the left side panel for you.
These rules include
If this booking breaks the cover limit you have set up. This will include the limit of the rule that is being broken, as well as how many covers are already booked in, including the booking you are adding- more info on cover limiters here
If adding two bookings into the same area/table with overlapping times or there is no availability in this table
When editing a booking in the expanded booking panel and this booking overlaps another
If the booking is too big for the table/area you're planning to place them in