I have had little trouble with binary systems, at least those with stars of dissimilar masses. The only significant problem I have had seems to be that anything orbiting BOTH stars soon ends up getting ejected into space.
I set the stars fairly close together (about 2 to 3 AU apart) and have chosen a late F-type primary (Type F8 or so) of about 1.2 solar masses, and an early M-type secondary (of about 0.6 solar masses, type M0.5). Orbiting planets close in to either star is not a problem, provided orbits are close enough not to be significantly influenced by the gravitational well (Hill sphere?) of the opposite star. In my particular simulation, the single habitable planet in the system orbits the secondary at a distance of about 50 to 75 lunar distances (about 0.14 to 0.25 AU?).
Now, getting a moon to reliably orbit that habitable planet---That's another story entirely!
I've never figured out what the "lock in place" function does, other than to lock a primary star into one position so the entire solar system doesn't drift through space. It didn't strike me as particularly useful, though if it helps with getting binary/multi-sun simulations to work properly, then it may be worth using, bearing in mind that, in reality, the stars do NOT remain fixed in space.