Sometimes tail bags can cause the matting process by rubbing on the tail hairs because the tail is able to move freely within the bag. That's why I wrap my tails up using vetwrap instead. I still need to take them down at the beginning of winter and the end of winter as well as once or twice in the summer to rebraid and rewrap. With no flies in the winter the horses/ponies tend to flap their tails about less and so fewer take-downs are needed. In the summer however you need to keep a closer eye on it.

"Oh, we are but soft and squishy bags of mortality rolling in a bin of sharp circumstance, leaking life until we collapse, flaccid, into our own despair." --"Fool" by Christopher Moore