The aux fans are there to prevent excessive high side pressure. On many cars they are not turned on except by the high pressure a/c switch. With a/c off they very well may not come on at all. This is normal.
The reason your tech is telling you this is that with the ACC on all the time, it occasionally kicks in the a/c compressor. By occasionally turning it on, the compressor seal is lubricated preventing an eventual leak. You can accomplish the same thing by turning it on once a week.