At first blush, it seems a no-brainer; who wouldn't want more range of motion, circulation, and all else that is promised? Just one problem: it usually doesn't deliver (especially when done as commonly taught in the US).
From a mechanistic point of view, it seems to make sense; if we want it longer, just pull on it a while, and it will eventually get there. Some more enlightened approaches attempt to fool the nervous system into allowing more length through distraction or use of the agonist/antagonist reflex.
These both miss the main point: How did we get here? Why is the tension, the limitation there in the first place? The body is far more than a lump of tissue, or a twitching mass of reflexes. There is very complex orchestration going on all the time. There is always a reason for things to be the way they are structurally. We may not ever find out what it is, and we don't always need to; we need to assume that there is one, or we will be fighting the body we are trying to change.
Instead of dictating what needs to be different: "longer here, more relaxed there!", I prefer to ask the body how it might accomplish what it is already doing, without restricting itself in this or that particular way. To be clearer: demand (but do not force) action and support in a direction or manner on the edge or slightly beyond the current natural range[see more on ranges]. Over time, the body will learn to expand its range of possible action and stability, and include the new range. (The skill of expansion is worth its weight in gold, as well...)
I'll use myself as an example. I've had a classic case of tight hamstrings most of my life (not awful, but limiting). Rolfing, stretching, martial arts, yoga, and dance all had some effect (Rolfing by far the most) but still the issue was there. In learning squats Systema[link]-style (vertical spine), and some of the other near-the-ground movement drills, I have far more freedom in my hips and thighs than ever before in my life.
These movements demand that I support myself and act through my joints, at odd and end-of-range angles and rotations. I never stretch; I merely move. It is not an instantaneous process, but the benefits are wide and lasting. I haven't increased my range of movement but my range of action; the intelligence and resilience of that whole area has increased.
Stretch yourself by expanding your capability to respond. That is something worth working for.