Can you imagine your sewer water backing up through your toilets and flowing out onto your floors? This has been the experience for some homeowners that had their sewer lines get invaded by tree roots.
While tree roots aren’t sentient, they have an uncanny ability to seek out nutrition, and if there is a minuscule leak from your sewer lines, the mix of water and fertilizer is going to attract some roots. Once the root has started to take in the nutrition, it won’t be long until it grows and forces whatever weakness there was in your pipes to expand, making the situation worse preventing the flow of your sewer line.
It is possible to clear up the roots inside your pipes, but you need to do a thorough job. Just cutting away the roots inside the pipe will only allow the problem to pop back up again later. You will need to patch the hole in the pipe so that there won’t be any access anymore to your sewer water.