While having the strength to support yourself in extreme ranges of motion is a major part of flexibility, a muscle's level of tonic contraction is the biggest limit on most people's flexibility. Static stretching does reduce tonic contraction temporarily and to a small degree, but it is not very effective at this. The best way to reduce a muscle's tonic contraction is through compressive techniques, such as body tempering and variants of myofacial release. A combination of stretching and compression actually works best of all (this is similar to the active release therapeutic modality).

As an anecdote, doing an hour of yoga every day for three months didn't do that much for my hip and shoulder mobility, but an hour of body tempering by rolling on a PVC pipe while watching TV (while doing absolutely no stretching at all) produced massive improvement.

Depends on the type of yoga too, I imagine. I've been rolling out my hip and practicing Bikram's yoga for a while with excellent results. One of the features of Bikram's is the number of "compression postures" but not sure if that's the same thing as what you're talking about...

Also for my hip (minor labrum tear).

Do you have any links you'd recommend on how to do what you did?

Take a look at this video: https://www.youtube.com/watch?v=Qq1z3usHseU

Those PVC pipes are ~$8 at your local home improvement store. I don't roll the way he does though. Instead, I try to move my body through various movements (squat, arms behind back/overhead, etc), and when I feel tightness or pulling sensations in the muscle I'll mark the spot. Then I place that spot on the roller, and just lean all my weight into it; I will roll around a tiny bit just to try and find the most tender spot, but once I find it, I hold still and press on it until it "lets go" and it no longer feels tender.

Once I had been using a PVC pipe for a while, I started doing the same thing using the shaft of a barbell - with weights on the end, it works a lot like a foam roller. This really hurts, but the results are amazing.

I really should make do a youtube video of this because almost all of the foam rolling/self myofascial release stuff on the internet is kind of bad. The barbell trick doesn't seem to be something people know about either.

Why is the video called "foam rolling" if just plain PVC with no foam covering is used?

Some hidden wisdom in here:

    Too much flexibility for a runner, on the other hand, may not be desirable. The
    ankle, knee and hip joints stay within the mid-range of motion during endurance
    running, so maximum static ROM will not have much effect. It has also been
    shown that stiffer leg muscles in endurance athletes may make them more
    economical in terms of oxygen consumption at sub max speeds (De Vries).
    Sprinting, martial arts, gymnastics involve movements of much larger ROM
    therefore depend on good flexibility. However, as already pointed out,
    development of flexibility must be specific to the sport. If a soccer player
    developed same type of flexibility as a gymnast, he would be of a greater risk
    of injury as extremely mobile joints may become unstable.

In your life or company, where you should be rigid or flexible really depends on what you're trying to accomplish.

The rise in popularity of "functional fitness" and its accompanying ideas about mobility and flexibility have made it seem like everyone should be a contortionist, but if you're only an amateur athlete, the mobility you should focus on is just what's necessary for your sport.

Like the paragraph you cited says, extra flexibility is sometimes a bad thing. Weighted mobility, once you can achieve the positions you need to, is a better progression than trying to increase ROM.

Anyone have any good tips/resources on how to achieve a leg split? ;)

Don't even try. I did martial arts for a long time. some people have the body for doing splits, some don't. I finally could do splits but I have quite a few injuries from that time. It's simply not worth it. Same for lotus seat in yoga.

Check out r/bodyweightfitness, I'm sure they have a bunch of good tutorials.