When should I NOT scale features
Scaling often assumes you know the min/max or mean/standard deviation, so directly scaling features where these information is not really known, can be a bad idea.

For example, clipped signals may hide this info, so scaling them can have a negative result because you may distort its true values.

Below is an image of 1) a signal that can be scaled, and 2) a clipped signal that scaling should not be done.