NEGATIVE on what you "heard."

Evacuating a perfectly good working system on a regular basis introduces a much greater chance of contamination and problems than just leaving it alone.

If the system is tight and was properly evacuated and charged, there is no way that any contaminants can get into the system. Even if there is a leak, there is no way contaminants can enter unless it is on the low side and gets so low on refrigerant or has a restriction that causes it to go into a vacuum.

The evaporator leaks can occur due to two basic causes. The first and the one that makes these evaps fail more than others is the fact that there is copper and aluminum that expand and contract at different rates. Contaminants or moisture have nothing to do with this type failure.

The second cause of evap failure is moisture in the system due to poor service. Poor service would mean a lack of drier replacement when the system is open and/or improper or inadequate evacuation. The moisture combines with the refrigerant to form an acid that will eat up the system from the inside out.

Soooo... If the system is leak free and has been properly evacuated you will NOT have moisture in the system, but opening it up for "preventive" evacuation and recharge introduces the possibility of moisture introduction and contamination.

That said, if the system was NOT properly evacuated, then it should indeed have the charge recovered, filter/drier replaced and PROPERLY evacuated and charged.

This is the epitome of "if it ain't broke don't fix it!"

Have a great day,