I understand how to use them, on an individual basis. My problem is incorporating them into an army. The Leningrad is a perfect example of where you'd have units setup specifically for that kind of job, either that or you'd change your unit layouts to play to the strengths of that terrain, because you can expect to be getting enough advantage out of the improved firepower to make it worth the effort to do so.
However, look at (as an example) the entire World at War scenario. There are some obvious areas where you might specifically design units, in relation to Rifle versus SMG components, such as the initial Russian offensive for AG Mitte, Japanese units in China, invasion of one-hex town/fort islands, and so on... I can understand that part. What I'm having problem with, is how to deploy them in general throughout my forces over the course of the scenario.
In the past I've always tried to go with a 50/50 split of Rifles/SMGs in all my Infantry groups as a general rule under the assumption that the occasional attack in a plain/swamp/mountain hex is offset by the occasional attack into a forest/urban/fort hex. That is what I was trying to get across, that I've found that to be inefficient overall in my personal experience against the AI, and have started using a unit or two of SMGs only (well, typically with Mortars and the ocasional infantry gun/machine gunners) per front-line HQ that I use when I can play to their strengths and leave my other infantry/armor of just Riflemen (and supporting elements). However, the reason I asked the question here, is because doing it that way feels wrong to me and I was wondering if others had an opinion on the subject.