It’s a misconception to think the benefits from practicing asana (the physical poses of Hatha yoga) are only achieved by being able to successfully do the pose.

A large benefit is within the process of learning what physical and mental techniques personally help you best to develop progress in the poses.

Example: the full/complete pose for a forward bend would be to touch your forehead to your upper shins with straight knees.
However, many people who don’t stretch their hamstring muscles regularly will likely not be able to even touch their toes.

Does this mean they get no benefit from practicing a forward bend?

On contrary, regularly practicing the pose, regardless how far they can go at moment, is the only way to start developing some flexibility in the hamstring.

Be clear I can’t promise that any amount of practicing will allow you to one day get your forehead to your shin, but it is certain if you never practice it regularly, you will never get farther than where you are now; Plus as you age over the years, you will likely become less flexible.

As the other poster mentioned, a good instructor will show you ways to modify any pose towards helping you eventually progress further into it.

Namaste’,
dwb

Despite the common misconception, yoga is not all about flexibility. It is mainly about building strength, and if you;’re flexible, that’s an added bonus. Most yoga classes should have different “levels” of the poses, so even if you’re unlfexible, the instructor should be able to show you a modification to the pose that you can do.