AFAIK it is currently not really easy to override the default-target-url. Sure, if you try to access a protected resource, after login, the application passes you to the requested page. But if you need to login just to get session info (imagine an AJAX scenario where certain functions can only work after getting a user session based on login), it is less easy. Of course you don't want users to return to the homepage. You can write a custom filter to prevent this, but why not make this a no-brainer? It is, after all, a very, very common use case.
By allowing users to add a spring security specific form variable with a targetUrl life would be much simpler.
<input type="hidden" name="j_default_target_url" value="http://xyz/something/">
When Spring Security encounters this value in the login form, it will take this value in stead of the configured default target url.
And life is simple again. Now, on to writing that filter for my current application.