I learned the power of saying things out-loud when I was in “the box” (a Redbird, but close enough for us GA-ers) and the instructor failed stuff on me in IMC and I had to actually use the words “I’m declaring an emergency”. I had never actually used the phrase before (thankfully because at that point, I had never actually needed to), and it felt ominous…even though it was only a simulation and wasn’t real. Since then, I have most of my clients actually have to say the phrase when we’re simulating an emergency so they can get used to what it feels like to do so (and what it’s like to hear themselves utter the phrase).
As for my own experiences, I had to declare once (not getting full power in a Warrior on takeoff - it ended up most likely being carb ice and a bit on the backside of the power curve from the student’s takeoff) and had one declared on my behalf one other time (also by NY approach). In the case of the non-declared one, I experienced engine roughness on an IFR (in VMC) climb-out passing through 5000’ that wasn’t due to a mixture setting or carb icing. I had plenty of altitude, the engine was still running, it was practically severe-clear, and there was almost no other traffic at the airport, so I didn’t feel it required priority handling…other than wanting to stay at altitude longer.