Happens all the time, both inadvertantly and purposefully.

If it's the last leg of an itenerary, and you don't get on the plane, big deal. The standby's move up the list. Maybe a preferred even gets your upgrade.

Getting points for the lost segment is another matter. Probably yes, because the system already has you 'checked' in. Personal experience says that yes, you'll get the credit. But I've only done it once in a while. I typically use my entire tickets.

But be warned that your no-show might get noted somewhere. Airlines are known for tracking customers who have a habit of not using segments of their iteneraries.

They have no legal recourse, however, to go back and bill you more $$$.