The basic thing to know about it is that it is made of rolled up tar paper with press together joints. As such, roots could penetrate the joints and fill the pipe, but in addition, the weight of the covering soil often compressed the pipe into an oval or even a figure 8 form. Plus, roots growing on the outside of the pipe can indent the walls of the pipe. Therefore, the main thing to know, is that if you have it and it is giving problems, the only long term solution is to replace it.