If you have boxes and boxes of tape, rubber bands, etc, you may not want to track for quantity for each one of those items.
Said another way, if I have 100,000 rubber bands, I won't need to know I only have 99,999 if one goes missing, because I can always buy more.
Using that same example, I wouldn't need to know if I'm ever overbooked or sold out of rubber bands, as they're easy to replace.
You can choose to disable quantity tracking when adding or editing your items.