I have a conjuctival nevus on my left eye? will it be beneficial to remove it? will it leave any scar?

Depends: You don't have to remove it if it's been stable for many years. If it is growing in size or changing in shape and may not be a nevus anymore, it is good to remove it. You could also do it for cosmetic reasons. If addressed properly, there should be no visually significant scar to the naked eye. That really depends on how you heal and the surgical technique used.