No, I only do it when things aren't obvious in Moi itself. As in, it looks like you have two solids but they won't boolean, so why not? have I confused Moi in some way? Are my control lines on my two objects touching? No? then I take it to another package to see if it can do it. It's a quick way to check errors. IE, 123D will show normals are not all facing out by assigning two colors to your model. If normals are not all facing out something is wrong with the solid. cad assistant will mangle the model so it will be obvious where things are wrong. Moi can on occasion do the same if you import from other software packages. what will come into moi mangled from lets say a solid works generated file will open up fine in 123D ( or, more to the point, open differently, some errors in moi won't be the same as the errors in 123D). I don't know exactly why but I suspect it has to do with each package calculating the model differently. You will need someone who understands this better to explain it.