The word "benign" means not harmful. Generally the risk of trying to remove a benign tumour is greater than the risk of leaving it. However, periodic checks of the tumour should be carried out, just in case it gets worse.
It would be dangerous enough. The tumour could be compressing on a fairly important part of the brain (ie. The brain stem - Controlling involuntary bodily functions, like heartbeat/breathing) or the optic nerve, leading to vision problems.
The only difference between a benign brain tumour and a malignant one is that the malignant one could spread to another part of the body, the benign one can still damage the brain.
Chemotherapy or radiation, or even surgery are the main treatments for benign brain tumours.
Hope I helped :)