If sites are self-provisioned or there is a request form anyone can use, then it's typical that users choose addresses similar to site titles which, unfortunately, change from time to time, mostly due to organisational changes.
I used to say "no" to such requests and we even have put governance in place to restrict changing URLs, so only business critical changes could be progressed. But recently a colleague of mine found an out of the box feature that some SharePoint administrators may be forgetting about.
The thing is that you can easily change the URL of any sub-site from Site Settings > Title, Description, and Icon. This page gives you the option to change the address online!
Changing the address take a second or few as it the actual site is not moved and its GUID remains the same. It's just the address being changed like a property.
This works on 2007, 2010 and 2013. The funny thing is that there is no such option for a site collection and that's why I thought the same is for sub-sites.