Friction can be bad by being too strong or too weak.
Sometimes, when it is too strong, it decreases efficiency since some energy is wasted and turns to heat. Friction can also damage equipment/objects like when you slide it on the floor.
When friction is too weak, like for instance when there is black ice- our center of gravity is displaced too quickly and we can fall. Likewise, if there is a lot of slush on the ground, cars can slip and slide.
