Oh dear... The LMBs are basically where the younger part of the fanbase congregates. It's not bad per say, but stuff there is often really immature and thus kind of off putting for all of us "sophisticated"/s teens-twenty year olds.
It also depends on what category you're looking in. The Bionicle category there isn't all that bad, albeit full to the brim of hit or miss fanfics and "HOO WILL WIN BONKEL VS HERRO FACTROY!!11!!" topics.
Ninjago has a little more when it comes to the immature things, like "Ask *insert obscure or poorly represented character here", "Ninjago fangurl hangout!!! XD", and "NINJAGO ROCKS WHY HATE IT"
And then Chima's... Well... Yeah. I think you can figure out what kind of stuff that yields.
So yeah, the LMBs are a good place for younger kids and somewhat amusing to browse(despite the immaturity). All around, I'm glad they exist. My username on there is "PensiveSamurai."