I used to do a lot of road walking at night so that was the main reason i had it. I also wear greens and browns when i am out, including in the mountains so if i come across a casualty or i become one i would put it on to help attract attention. If i was injured whilst out with my wife she knows to put it on and then summon help. If you have and ambulance crew or MRT looking for you it makes life a little easier for them. It is important to realise retroflective tape is visible by night viewing equipment even when they are not shinning a light at you.
I dont have the need for a VS-17 signal marker and to be honest it would not be much use here but if you are in a situation were you need to be seen why not make it a bit easier for those looking; a hi-vis vest is an light cheap effective way of doing this.