Well, our garage opens to the front of the house rather than an alley. If it opened to an alley, it probably wouldn’t get used as much.
Mainly I end up using it if I’m doing something outside and need to get something out of the garage. If I’m out front, I probably have the garage door open, but if I’m in back I don’t. The only way into the house from the back is a sliding door which can’t be unlocked from the outside (and has very light colored carpet in front of it, so I need to take my shoes off if I go in that way). So if I need to get into the garage, I have to walk around the house, around the garage, in the front door, through the laundry room and finally get to the button to open the garage from the inside. With the keypad, I cut my walk almost in half. Ok, so maybe I’m lazy 
It’s also handy if you’re outside without a car and want to close the garage door. It eliminates having to go back through the house to get out after closing it from the inside. You can go on walks without having to take a key, because you can get back in through the garage. Similarly, if you forget or can’t find your keys, you can use it to get in that way (good to still have a backup key somewhere in case the power is out, garage door opener is broken, etc., but for the every day case this works well).
We’ve also used it to give temporary access to the house without giving out a copy of the key. For example, we had our master bathroom remodeled a while back. We gave the contractors a time-limited code (different from ours) so they could come and go and we wouldn’t have to worry about extra copies of our key floating around out there. We also let visiting family members get in and out of the house that way.
Admittedly, none of these are Earth shattering improvements in quality of life, but they make things a little nicer.
Regarding the durability of the belt, we haven’t really had ours long enough to know if that’s an issue (I think it’s been about 4-5 years now), but replacing the belt wouldn’t be very hard if it did wear out. I don’t think I’d personally consider that to be a major factor in a residential application (reasonable size door, only cycled a few times a day).