Here is a link to a great article that sums up the reasons some people may choose cloth diapers over disposables. It's really long, so I'm providing the link instead of copying and pasting the whole article:
We bought a Bum Genius diaper on Friday just to see what they're like. The store only had green, so we only bought one. This is an all-in-one one size fits all cloth diaper, with a waterproof polyester cover and organic cotton interior. The manufacturer says these diapers fit babies from 8-35 lbs. Here are some pictures - these are not the cloth diapers our moms used!
These have elastic sewn in on the leg openings and the back. It has a full strip of velcro across the front to make the size adjustable. It has two velcro closure tabs, and two inside tabs to close the velcro tabs with when washing the diaper.
Here is the inside. It has a sewn-in full cotton liner, and two cotton "inserts" that are sewn in at the top and bottom, so you can adjust them depending on the size of the baby. You can also buy additional inserts if your baby needs them.
You can see the three rows of snaps in this picture. This is what makes the diaper one size fits all - you snap it up for smaller babies and leave it all the way unsnapped for the biggest babies.
We are very comfortable with our decision to use cloth diapers. We know it won't be the easiest thing to do, or the most convenient, and because our baby will be in daycare while we work, our baby still might have to have disposable diapers on at least some of the time - but we think we are making a good decision and we are going to try our best to stick with it!