Messenger type gives these bags their starting characteristics, which are size, shape and working mechanism. Their popularity in schools comes from the fact that rectangular shape of books and notebooks is matched by the shape of the bag, allowing for maximum ease of storing and retrieving.
The one of the greatest aspects of canvas messenger bags is the ability to be customized. These items find their place among the younger crowd, the one that needs customization the most. You will almost never see two identical ones carried by different people. That just goes to show how fun they are to work on. I had a green, army looking canvas messenger bag when i went to school which was, by the end of it, completely covered in signatures. End result looked really cool, i had all my friends do their signatures on it and everyone had different ones. That bag became one of my favorite items and i am never going to throw it away, no matter what my wife says.
You can do literally anything with these messenger bags and make it look cool. Also, you may get to love canvas as a material. It is light, it folds beautifully and bags made out of it have more applications than just carrying stuff in it. I will not go into detail of such applications but just let me note that this bag was used as a makeshift pillow for example. Another advantage of this material is that it is very durable and sturdy concerning how lightweight it is. The problem can only occur if you plan on stuffing heavy things in it, since strain on canvas can permanently damage its structure. Leather will allow for some stretching while retaining its original state but with canvas that is not really the case. If you stretch it too thin, you will permanently damage it.
Big problem of these bags are stains. There is nothing worse than having your ultra cool bag ruined by an accident. Unfortunately, you cannot do much about it except take extra care. Nowadays you can buy ones that are somewhat stain resistant but then you are not really buying canvas, you are buying some other similar material. I would recommend you not to get overly attached to any bag, since the biggest advantage of canvas messenger bags is that they are dirt cheap. You can always buy a new one and start the process of customizing anew. This can also be a lot of fun, you can keep the old bag for memory sake and proceed to make the new one even better!