I'm not an electrician. But I'm a nerd who has friends who've done forensic electrical engineering work. Here's a different perspective from above.
It's been code for like, ten years now, to use a torque screwdriver to tighten down the wire binding screws on outlets. Some of them take a surprising amount of torque! 18 in/lbs is way more than you think. This became code because Aronstein found countless failures and fires caused by poor threaded fastener binding connections. Many connections made by licensed electricians.
In other places, some have tested electricians in large numbers, and found something like 70% under tighten when done by hand, and 10% overtighten when done by hand.
Using a calibrated tool to apply the specified torque is the only way to ensure (1) the wire makes proper full contact initially, (2) that you make full contact without damaging the threads, and (3) that the connection stays correct for the next fifty years, and while under the extremes of it's uses. If it's under torqued, resistance will always be higher than it should be. If it's under torqued, the screw can definitely slowly loosen over time as thermal cycling from high loads causes the metals to expand and contract. If it's under torqued, you may also not fully penetrate the surface oxides.
If you back wire with pressure plate connections, you face all these problems, but worse, since friction is the only thing holding the wire in place.
If you use trash residential grade receptacles, all of the above problems are magnified greatly. If you use high end spec grade (or even "extra heavy duty hospital grade", as I prefer!), Then you have a tremendous factor.
Apparently, all this is why the code is moving towards pigtailing.
My advice to you, as a non-electrician to a non-electrician: if you're NOT using a torque screwdriver, aren't using high end receptacles, don't have AFCI breakers, and aren't testing the resistance of your outlets with a nice Ideal Circuit Analyzer, then pigtail with a high grade wire nut. You'll probably appreciate this at some point in the future. The ideal Mini Twists are nice for cramped boxes. 3m makes really nice fancy winged ones if you have space. As a non electrician, I find it hard to pretwist the wires without doing more harm than good! The instructions always just say "line em up and twist nut until wires themselves start to twist".
If you're an electrician, just please God go buy a goddamn torque screwdriver, and use it! They're now like forty bucks on Amazon! I've yet to see an electrician use one. It's code. It's also better for your customers. It takes like 3 seconds. I beg you. Do it right!