Tower Controller relieving the combined Local Control/Ground Control positions noted that the Controller being relieved was using inappropriate applications of LUAW procedures.

Narrative

I had just entered the Tower to relieve the combined Local/Ground Controller. The Controller had B757 in LUAW on the runway. A heavy B777 had just departed. Normally; the rules say do not position-and-hold (LUAW) behind a departing heavy to wait for appropriate wake turbulence spacing. Anyways; I realized that LUAW was being used by combined Local/Ground Controller when it is specifically banned in local/national orders; operational AMASS notwithstanding. I queried the Controller; probably less than 4 years in FAA; and he suggested it was no big deal. The other person in the Tower was CIC/Clearance Delivery and perhaps was unaware that LUAW was used inappropriately. Recommendation: keep scrutinizing the young/hotshot/lazy controllers; especially those who aren't fully aware of the consequences of picking which rules to ignore and which to follow. It wasn't entirely clear that he forgot the rule; forgot he was combined Local/Ground Control; or 'implied' that he'd decombined Ground Control just so that a really unnecessary LUAW could be issued.