Resting your body is an integral part of any exercise process.
Sometimes rest is planned. It looks more like "a day where I am not exercising" because it is not a part of my scheduled process. That right there is one good reason to rest - to strategically avoid over-exercising and to give your body ample active recovery time between exercise sessions.
Then there is the grey area of rest. The one that has to do with you and I and how we feel on a day where exercise was scheduled.
If you find yourself thinking "I'm supposed to exercise today, but I don't feel like it," then you might have a problem that you need to address. Sometimes the solution is as simple as finding that little extra oomph - close Netflix, get out of bed and do what you had committed to doing.
It can be more complex though. Maybe you have an issue with the place or person facilitating your exercise. Perhaps you simply dislike the particular exercise that you are scheduled to do. Maybe it is a workout that has had you feel unnecessary pain in the past. Your family might not be supporting you in your exercise efforts.
These problems are numerous. Address them directly as soon as possible so that your exercise process can help progress you towards your functional, health and aesthetic goals.
In the other part of the grey rest area, a workout is scheduled and you find yourself thinking "I need more rest". This is vastly different than "I don't feel like it". The former is an avoidance effort; the latter is an alert that your body needs more recovery time.
Listen, adapt and facilitate yourself appropriately.