There's no way you're going to tell your mom that URL over the phone. You're gonna have to email it to her, or in the worst case, drive over to her house and type it in for her if you want her to visit it. After you're done messing around on the computer, she's going to make you hang up that picture frame you've been promising to hang up for her for the last three weeks. Thus, most of the time, we'd like to avoid URLs such as these. Such is the case with my fictional hideous example.
Different systems deal with query strings differently.
This also makes a query string a natural place to stuff values for arguments to SQL Methods. SQL Methods generally rely on some sort of argument in order to return useful data. Now, we can call a SQL Method from DTML with arguments. But obviously we can't have people type DTML all the time to get a result to a database query. So we've constructed a general-purpose combination of a DTML Method and a SQL Method that can return different results to the viewer based on arguments inside a URL query string.