I suspect most of the engagements we play during the game represent the very worst fighting (apart from a few huge campaigns that it would be difficult to get enough models for, and then you'd need the space to do it) a space marine experiences.
Actually, what do Space Marines do when they're not fighting hive fleets, traitor marines, or some of the nastier xenos species (Eldar of both varieties, Necrons and the Tau are starting to become more recognized threats)?