Depending on your class schedule, commuting can be really difficult.
Some days you will start at 8:30am, and it's likely you may not finish until 10pm if you have night class. This means you'll be at school for over 12 hours on these days.
Or, you could have the flip side where you have one class, and then an hour or two (or more) break inbetween. It's not worth it to go home, but it's irritating to stay on campus.
The commute itself (depending on where in Mississauga and what method of transportation you're taking) can also be up to an hour, one way. That can be a 15.5 hour day...not fun in the least.
Meanwhile, it can be a lot cheaper, as you may not have to pay for room and board as well as food if you commute.