You can manage inventory regardless of whether you are doing Assigned Seating or not.
If you use Assigned Seating, simply specify the range of seat numbers for a seating/price zone and we will keep track of inventory.
If you do not have assigned seating, you can still setup seating zones such as VIP, Regular, Standing, etc. and assign upper limits on each zone. You can then create multiple ticket types within a seating zone, such as Early Bird VIP, VIP, and Group VIP that all pull from the same VIP seating zone inventory.
Your event campaign dashboard shows you the inventory status in real-time!, including seats site visitors have in cart at the moment.