For example, for Star Alliance flyers, until recently (yesterday in fact) you could achieve Star Alliance Gold status (priority check in and boarding, free checked bags, first to be upgraded, last to be bumped, lounge access, etc) for cheap by registering for Aegean Airlines' loyalty program as they only required 20k miles to achieve Gold status whereas most other Star Alliance partners require 50k. You could also keep this status for 3 years as long as you logged some miles each year (other airlines require you make the 50k level every year.)
Yesterday Aegean too announced revisions to their loyalty program which pretty much put an end to this. But there are still other loopholes in other airlines' programs being rooted out by the dedicated.