In that particular case? First, because it was the best avenue of advance (best payoff, least number of orders, juiciest targets, etc.). Second, because a Rafiq sprayed the SAS off of the Maggy in the following order using Triangulated Fire. It's easy for a player to engineer a situation where a TAG has to pass within 2-4" of a camo marker (with respect to units with Kinematica) in order to cover its ideal route of advance. It won't happy every time, but that's what Engage is mainly used for in my games - tying up a unit that will either attack my unit with a DTW, or tying up a unit that probably has a poor chance to win the Engage FTF roll using a normal BS weapon.