Two yoga students, three opinions. Rule one is "who do you listen to".
Benefits comes from sound, disciplined, continued practice.
Relative to stiffness in the physical body it follows the thoughts, actions, and nutrition it is given. If you sit in a chair for 8 hours a day and expect to keep that damage at bay with some occasional stretching you are self-deceived. The behaviors need to be altered and the asana needs to be adhered to.
Asana, at least within the alignment-based practice I study, teach, and practice within has been highly refined. Poses individual has physiology and psychology. They also have a cumulative effect when they are properly sequenced - a negative one when they are not.
To many cooks spoil the stew. Find a sound teacher and follow along, balancing both discernment and trust. To take in ingredients from too many sources can only muddy the waters. How one breathes in daily life, how one breaths during practice, and what one might do WITH the breath during pranayama ... these are different things.
Learn how to open the home of the breath, learn how to maintain a smooth breath when practicing, and learn one or two gentle pranayama, then practice them for the first ten years or so before moving on.