We had this very conversation this afternoon. The conscientious pilot who will fly us tomorrow on a test flight, expressed concern to me that a proper run up will be difficult, as the ramp really does not accommodate that well. We've done it before with great caution, but congestion, passing taxiing aircraft, and the prospect of noise make a ramp run up just seem thoughtless. This European airport only has one runway, and associated taxiway, so there is no out of the way place to practically taxi for a run up. I suggested that we take note of any other aircraft which might be departing, and let them go first if we can, then, with no one behind us (hopefully) on the taxiway, as ground for a delay on the taxiway, before we pull onto the runway. The pilot seemed reassured that this was a reasonable request. I'm confident that a ground controller will accommodate a delay, if we can find a way that it not inconvenience another flight.
For my choice, I will sometimes do a run up on the roll, if I'm comfortable in the aircraft. But, it is entirely fair that a pilot choose the confidence of stopping entirely if they want to apply their full attention to the aircraft systems. Though a long time ago, I devoted too much attention eyes in during a run up. I was running up a C310, and cautiously holding lots of brake pressure while I looked at the gauges. It had been a while since I'd flown it, so I was being thorough. I noticed in time, but none the less alarming, that the aircraft had been slowly sliding forward on the slightly snow covered pavement. No harm came, and I still had room to turn and taxi away, but I could have slid it off the edge onto the grass, had I not looked up. So, yes, lots of awareness for what's around you, and is something changing!