For a long time, I’ve been using MLCad to design specific details on mocs I’ve been building, but since December, I’ve begun designing complete craft directly in the program.
So far I’ve only found two of these designs worth rendering in lego (this and the black fighter crashtested a while back).

But I can definitly recommend this approach: firstly because designing is much faster in MLCad (or on paper), so generally you’ll have many more designs to choose among, once you’ve finally got the time to pick up the bricks, and secondly, you’re sure it’ll actually work, unlike the ‘vague idea that might look good’ that is the usual starting point when we design directly in lego:

Concept art mocs almost always pwns anything we can design directly in lego, but more about that later, when I’ve finished my colourscheme-investigation