When it comes to desired traits in fitness, raw strength and speed often overshadow mobility, or how well your joints move. Maybe you just don't think you're that "bend-y." Fortunately, it's a process that contributes to strength, and everyone can work on it.
Mobility is different from flexibility, and in general, having good range of motion lets you exercise and perform everyday movements (like getting off the couch or reaching behind something to plug it in) better. Mobility exercises, then, let you actively improve your strength, control of your body, and range of motion all at the same time. This video from Calisthenic Movements explains that if your joints move only in a small range, you are basically limiting the development of strength and muscle from your exercises. If you were ever to "accidentally" move beyond your limited range, you could hurt yourself, and no one wants that.
If you want to work mobility exercises into your routine, incorporate them into your pre-workout warm-up, or do a few simple drills on your rest day. To start, check out this awesome one for hip mobility (great for runners too!).
How Important Is Mobility? [Calisthenic Movement]