No one with half a brain is going to start first thing doing any serious compound exercise with out stretching/ joint flex and having blood flowing in an area. Started many workouts with heavy PBN's (one of my favorite exercises) but will stretch and warm up the shoulder girdle by repping out for 30 to 40 light reps maybe for a couple of sets. And with just an exercise bar, for full ROM. Best way to warm up before attempting a heavy compound exercise (for me any way) is by doing that exercise. Also fires up the muscle impulse motor units that are to be used, which can help greatly with smoother exercise performance. Will usually include straight arm pullovers (light) for a complete stretch/warm-up of the upper body/shoulders also.
If anyone is doing PBN's with the grip too wide (or too narrow) or lowering the bar lower than the nap of the neck (common range now a days is a little lower than the ears, which falls into the partial rep area) than for some you may be inviting trouble.
The Smith does not allow the natural "S" curve when pressing overhead (include bench/inclines here too, as well as squats & DL's). But you could use it for short range partial training. Of course a PR is first choice by far. Full compound ROM's may not be followed if worried about potential joint/muscle inserts problems soon or later. A Smith can be used by a lot of people who train with lighter weight, but for heavier compound stuff, may be not the best idea. Just my view, that's all. Good Luck.