It is a good idea to change your workout plans every so often to get out of the rut of doing the same workouts all the time.
By changing the program it keeps things interesting and allows your body to continue developing.
However, if you follow the same workout for a prolonged period of time it is very likely that one of two things could happen:
1. You might get bored and lose interest in training due to the monotonous workouts.
2. You hit a plateau with your progress due to the muscles being used to the same type of training and exercises.
If you notice that you have experienced either one of these instances mentioned above then you could benefit from changing your workout plan.
In my personal experience it is a good idea to re-evaluate your goals and progress every twelve weeks and change the training program accordingly.
Also, it is also advantageous to mix up the exercises, as well as change up the sets and rep ranges from one workout to another to keep the muscles guessing and shock them into new growth.
I have used a variety of training programs and methods over the years to keep it interesting and purposeful at the gym. This has definitely contributed to continuous improvement for me and is a tip for helping others also. Some of those programs can be found here: https://www.sashoognenovski.com/shop--cart