For me personally I have found poles on the flat to be a complete waste of time and in fact something of a hindrance.
Online instruction videos for walking poles often mention this - "propulsion" that poles can provide when used in specific ways, but probably isn't required for general hiking. 'Fast and Light' long distance hikers may find use for it to ensure they cover major distances in a day, but on occasions where a pole has been used on the flat in a proper way, that very efficiency narrows me into a groove of momentum that once snapping out of it later seemed unnescessary and has only served to burn off way too much energy reserve.
It may get me there 30 mins earlier, but at what cost? It is for this reason that like you I don't use a pole 'properly' (
as in, close to the body, angled and driving me forward) when on flats. It is in my hand, but used as a 'feeler' (one of the great pluses of poles, I reckon) to test terrain in front of me.
Like you, my real use for a pole comes on descents. It was the core reason one was bought, after a self imposed knee injury which meant that four hours into any walk after that, the knee would start playing up and make the fifth hour a grimacing snail's pace. Using a pole helped hugely and my belief is that it aided in what proved to be a natural recovery over a few years.
Having said that, I think it is also easy to over trust a pole / poles for descents. Doing so nearly led to a horrible accident when hiking alone in Norway one year. Wedging the pole in, my trust was too quick and all of a sudden its hold flung away just as I was putting weight onto it, due to hidden ice in the placing point. I fell forwards off a drop, at an angle, with a backpack on. It is a miracle that a leg wasn't broken or the pole head didn't impale me in the side on landing (miraculously, upright).
Ever since then, I keep a carefull balance between my own security and what a walking pole can provide on descent