Shower head gets dirty due to bacteria, minerals. It gets rust inside and interrupts regular flow of water supply. It’s really uncomfortable during your shower time if you don’t have good water supply from shower head. Excessive bacteria or minerals cause skin diseases if you regularly use water from dirty shower head but it’s invisible with naked eye.
You will get skin diseases eventually if you use regularly use water from such shower head. So for your sake of health you should regularly clean your shower head.