Chad, This is a great question and a complex one with a lot of historical misinformation IMO. If you asked 10 coached this question you would get 11 different answers. Heres my take. I approach this differently depending on WO type to some degree.
For Zone 1/2 aerobic training: Little to no solid evidence that pre or post-workout stretching produces increased performance, decreased injury, or enhance recovery. I don’t stretch here or do any special dynamic WU. I start out slowly and bring up the effort to desired level of 10-15 period. If its a sub 2 hours session I usually don’t do much of a cool down. If it’s a more extended session and I have time I will do a 15-20 walk at the end. Some days I will walk for 15-20 min at the end of the day as well to aid recovery. Dogs are good for this.
For high-intensity training (intervals or ME weighted work) These are a different story a bit. I think a more well-planned warm-up is valuable here to get ready to try hard and get the most out of the workout. For interval type work I will do the 15 min ramp up like the Z2 days then throw in a short set of 2-4 30 second pickups to a faster pace to get all the neurons firing and make sure I am ready. This works really well for me. For 1 hour of heavy weighted pack carry muscular endurance type work I will commonly spend the first 5 to 10 minutes of the weighted portion slowly ramping up as well to let my body get used to the weight and the effort involved.
With regards to stretching for general flexibility (as opposed to warmup) I do perform a fairly specific set of stretches 2-3 Times a week as a separate work out to maintain or ideal improve my flexibility for specific rockclimbing goals but I do those as separate sessions apart from the aerobic training and without any intent that they are going to improve my aerobic performance.
Hope that helps!