No filter… bad idea. You just turned your evaporator coil into an amazing “filter.” The evaporator coil is wet and without a filter installed, all the dust and dirt (even in the cleanest of homes) is being circulated and collecting on the coil–which in turn will cause the coil to be restricted and result in system malfunction.
Second requirement is for the health and well-being of occupants. A higher efficiency filter will provide cleaner air but will your system support the higher air flow restriction put on your system?
Your existing indoor unit (air handler) in most situations is already struggling and under-performing due to an undersized duct system. So, with good intentions, you install a pleated filter that is now making a bad situation worse.
Most pleated filters are a disaster. They require close to 50% of your air handler’s ability to move the proper quantity of air (CFM). Therefore, destroying your energy costs and premature failure of your air conditioning system.
In order for the homeowner to know what filter their air conditioning system can support, have your air conditioning technician test your system to find the total static pressure that your system creates without a filter. The difference between the manufacturer’s listed maximum static and the total static test that was just performed will tell you what filter to install.
Tip: Install a low efficient low static filter and spray it with cooking spray “Pam”. This will improve your filter greatly.