There are many reasons you might want to add some space to your yoga practice.
For taller yogis over 180cm, or those just desiring more space for their practice, a long yoga mat may be the right choice for you. As you move from standing, to seated, to reclined poses, a long yoga mat gives you more room to move around without hanging off of either end of the mat.
In general, a long or wide yoga mat serves those participating in more active or diverse practices, like practitioners who use their mats for other fitness activities or for those partaking in more restorative practices that necessitate many reclined poses. In addition, a long yoga mat serves those who are tall and often find themselves off the mat during reclined poses. Those practicing outdoors may also find benefit in a large yoga mat or long yoga mat, so as to better keep themselves off the ground during all poses.