When you see with both eyes, then binocular vision is present and depth perception is good. On seeing with just one eye depth perception is not good and you can have difficulty say in assessing the speed of an approaching car. But you can certainly use just one lens in an eye if you do not have any problem like headache or double image. I hope it helps.
No, it won't weaken the other eye. You can use it in just one eye if you want. Thanks.