A Post-Patch Perspective: Roach Baneling ZvT (Starcraft 2: Heart of the Swarm)
Until the most recent patch, I, as well as most other Zergs, had a serious issue with Widow Mines. They were built quickly, and provided an unpenetrable defense at most stages of the game. Once a large enough number of Mines are produced, they could be easily switched into an offensive unit, as well. With just a handful left at home, entire armies could be decimated during run-bys at key choke points.
The Widow Mine nerf changes everything drastically. Terran players are now scrambling for any kind of build order meta-game that will allow them to stay alive against roach baneling aggression, especially in the mid-game.
In comes sir Taeja, who shows Terran players that Widow Mines are still devastatingly strong, but that gas openers are the go-to thing now--incorporating Reapers, Hellions, and oftentimes Banshees as well. These units are great at defensive postures against Roach Baneling, and allow for the Terran to limit creep spread and contest the Zerg third. Ultimately, the Terran can then tech switch into Stimmed Marines with Medivac and Widow Mine support, using constant drop tactics if the Zerg skimps on anti-air.