1) it was aesthetically pleasing
2) it obscured the view of our neighbor's house
3 and the bamboo remained bright green in the middle of winter . . .
but apparently, you are NOT supposed to let clumping bamboo grow in this fashion, as the rootball can get so dense that the bamboo can strangle itself-- you're supposed to cull the "weeping" culms and clear out the dead branches between the healthy upright culms-- so I've got some serious work to do, I trimmed some of the bushy stuff this morning, but I'm going to have to get down on my hands and knees and really weed out a lot of dead shoots and clean out the leaves (and soccer balls and dog toys-- I found a few of those in there) to allow air circulation and healthier sprouts . . . here's where I am now in this project, but I probably won't really get in there and trim everything until fall, when it gets colder and I won't get eaten alive by mosquitoes.