Automatic tuning will tune from channels 21 through to 69. The problem is some equipment will lock onto the wrong transmitter which means it is not the transmitter that the aerial is aligned to. This will cause the reception to be inconsistent and problematic. The main issues we get in the Southeast would be equipment tuning into the Crystal Palace transmitter as this is the first group of channels the tuning process would go through.
Manual tuning overcomes the above issues as some equipment can have the specific channel numbers entered.