There is a good chance that your messenger Chicago company uses a lot of bicycles to transport your light packages or documents around the downtown core. Bicycle messengers are preferable for a number of reasons, and we should all take advantage of them as often as we can. They are much more affordable, they are often quicker, and they are much easier on the environment. They also congest traffic much less for everyone else in busy downtown hubs. They can even be a faster means of delivering something. All these things are in the bicycle messenger's favor. Their only real downside is their definite limitations in the size of the packages that they can carry.
If you're not sure how large of packages you can send with your bicycle messenger, it's easy to teach yourself how to quickly recognize something that they aren't going to be able to carry. First of all, anything which weighs over ten pounds is probably out. Most courier companies have policies that ask their bike messengers to not accept anything weighing more than this limit.
Next, you have to use some common sense to realize that anything that is going to make a bike messenger unsafe, they are going to be unable to carry. Imagine yourself riding a bicycle carrying the object you want to ship somewhere on your person. If you think it would be impossible, it probably is.
Keep in mind that just because a package isn't over that mentioned ten pounds that a bike messenger won't necessarily be able to carry it. Size is a consideration as well, and something which is light in weight but huge in size is not going to make a very convenient package for someone to carry who is riding on a bicycle.
Bike messengers can be extremely useful, and are often the best choice for shipping certain kinds of things within a certain area. If you need to send a bundle of documents across the financial district, you can't find a better deal, or better service than your bicycle messenger. However, if you want to send all of last year's account books to the book keeper on the far side of the city, they might not be the best option. Practicality is the rule of the day when it comes to deciding what a bike messenger should or should not carry. When in doubt, just call the courier and describe your package to them.