Because of the sustained poses, yoga isn’t ideal soon before running. (See above about lessened muscle power following static stretching.) But I’m certainly not going to discourage any runner from an activity that can increase flexibility, balance, and body awareness.
Probably the greatest benefit of yoga for runners comes from balance poses, like the Tree. These help strengthen the small stabilizing muscles in your hips and butt that play a large role in running economically. The biggest caveat for a runner going into a yoga session is to always be mindful that you’re a runner first. In a class, you’re likely to be around people with greater flexibility on many poses, and the idea isn’t to will your body into positions it can’t currently handle to show off how fit you are. Go only to the point of gentle opening, regardless of what others around you or on the video you’re following along with are doing.