My only exception to not doing fecals is the "after the first hard frost". I only worm 3 times a year anyway, so I don't bother with fecals for the December worming (I live in a warm climate where a truly hard freeze in November does not always happen).
The last time I did take stool samples to the vet, it turned out that two of my four horses did not need wormed. I would have poisoned them for nothing and wasted two tubes of wormer, had the fecal counts not been done
The two that did need wormed were barely into the "medium load" and Tapes were evident
It was my two horses with metabolic issues so I guess the message is their immune systems have weakened thanks to their insulin problems