@krinid: I thought of that all the times, I used my legendary TS. But in many cases the forth border, if even available, was hard to reach. Either you had to lose the JS benefit, or you need one or two more territories.
Especially in the early phase of a level, where you really can gain lots of armies where an expensive territory connects with two or three cheap one. A good example I remember is the Far Land map, where you have in the north-east region of the path circle one big territory on both sides of the path.
So my decision was, lesser armies but more usages.

Fair enough, I have both @ Insane and sometimes trip them both. It's totally possible to finish levels using just TS, QS, IM, and it doesn't take that long if you manage to plan the territories right but it's super low effort