I don't cement my LR together.. they are arranged by stacking one on top of another.
the reason for doing so, is that it will allow me to rescape anytime. I add fish in slowly, so almost everytime i add a fish, i will rescape it (either minor or major).
I thank God that i decided to have a sand bed.
1) It looks more natural.
2) Deep or shallow sand bed, it is a form of filtration to your water
3) everytime a drop a piece of rock, I am reminded on why sand bed is a good idea.
4) Live Rock have odd edges, if you don't have sand, these edges will be resting on the glass, with extra pressure added when you stack the rock on top, and pressed on the glass at a point... i don't know when it will give way. With a sand bed, the rock rest on the sand, and the pressure is spread out.
My 2 cents worth, Sand is better than no sand. Dirt on the sand can always be managed. Broken Glass Tank, will be harder to manage