For the time when OS 9 was relevant that would have been a RAM hog. My iBook (first generation) had 32 MB RAM on board (plus an upgrade slot, how refreshing).
Sure, that wasn't top of the line, but it would definitely restrict your ability to multi task with other programs at the same time. My memory is that many programs used far less than that, allowing you to easily have 5-7 programs open (I had a RAM upgrade for a total of 64 MB).
Wow. As a comparison, I just opened a new Google Maps tab in Chrome.
According to the Chrome Task Manager, the tab alone uses 433mb RAM and 34mb GPU memory footprint after first load.
Sure, that wasn't top of the line, but it would definitely restrict your ability to multi task with other programs at the same time. My memory is that many programs used far less than that, allowing you to easily have 5-7 programs open (I had a RAM upgrade for a total of 64 MB).