LDRAW is for dorks
You can't make illegal connections in LDD and some parts are buggy, hinges are also a pain to work with sometimes and parts can be hard to find, but it's good enough for 90% of stuff (at the very least to make a quick draft).
I think you can manually position bricks anyway you want in LDRAW and can create your own elements if you're talented enough. I'm sure there are other neat things about it, I just haven't bothered using it since LDD does the job most of the time.
So like Hawkn said, LDD sucks for some things, just use what you need. If you're making normal stuff that doesn't require crazy angles and lots of articulation LDD is great, for complicated stuff switch to LDRAW.
It's a good idea to find a site or some people who like building what you do so you can get some solid feedback. If you post your stuff on general LEGO forums you might get some "Cool!" responses and some "Hey, why isn't this star wars related!?1!!1? STAR WARZ RULEZZZ!!!!".
From what little I've seen of the mech/robot community, the builders usually seem pretty helpful and will share building techniques, which is a huge advantage because mechs definitely use some complex (and often "illegal") connections.