Strategically, it can come off of Marowak's very good attack stat, assuming it's holding Thick Club, and break subs, as you mentioned. This could be the bane of very popular sets such as SubPunch Breloom and TyraniBoah, as well as other Pokemon which could potentially sweep from under a Sub, such as SubCM Raikou, which is usually faster and would OHKO with HP Ice. The immediate power from Earthquake is tempting, but Marowak has a very useful unique move in Bonemerang, while many other Pokemon can use Earthquake much more effectively. Basically, if you're going to use Marowak at all, use Bonemerang, as the slight accuracy problem shouldn't be too much to deter one from the other benefits it has over Earthquake.