i think of the very top as an opportunity to squeeze squeeze squeeze then fight the negative on the way down. perception can be a funny thing, if you're thinking the movement isn't helping or "oh, i'm resting," well, that alone will fuck it up for you.
the science of it will allow a rest at the top but i've always used preacher as a real mental exercise, used for creating connection. i like to use it near the end to pump blood and focus on the pump.
the plate loaded preacher benches are nice because i'll use drop sets until the finishing weight is small, then i'll do single arms, back to 2 arms, then manipulate my hands to create a focus and burn in different spots along the muscle belly.
again, i don't think of it as a mass builder per se, but then again if done to create a maximal stress or pump, who is to say it's not a great exercise for growth.
additionally i like to steal a mat of some sort to put on top of the preacher padding, something spongy like a yoga mat, this allows me to dig in better and go a bit heavier without worry that my elbows will slide out of posititon. lastly, i like to keep overtop the pads not leaning away or back, keeping my shoulders out of the movement. this anatomical set up allows for less angle for rest at the top as well.
i suppose you could rest at the top but the hope w/ all movements is that we think and our instincts evolve, causing us to act in ways which make movements more challenging and not easier.