Cleaning Shower Heads

Not sure I understand the recommendation to set a very low water pressure, cold drip cleaning the faucet and shower heads. If clogged, would not that affect both hot and cold? Other ideas, if only cold water just to come across?

Well, if your hot is coming through strong and cold is very low, although this is not your shower head - your cold water tap is not open all the way, there is an obstruction in one of the valves and supply lines, or the shower knob / handle is defective.