...And here's why
Due Diligence. The Lions and Jahvid best now have clear knowledge of the status of his head injuries. They know where Best is, and can better track what future concussions have done. This current, in depth, testing will be combined with his old records, base test, college history and with that, Best will be able to make a sound, well informed decision about his future. Also, the Lions will have direct knowledge and well documented information of how Best came to his decision to play and any pending consequences of.
Should he play?
When hearing a question like that, I find it best(no pun intended) to put yourself in that person's shoes. If I was a professional football player a couple years into the league and had a concussion issue... would I keep playing? hmmm... Tell you what... I probably would. Especially if I was explosive, fast, and an important part of the success to my team. Another reason would be... even if I quit now... I would probably still have issues later, but less funds to treat those issue. No, I would choose to keep playing. You only live once (yet to be determined) and not many people have the chance to be great. At least you gave it your all.
Lastly, if the situation was too dire... the Lions would have parted ways, like they did with Zack. It's all about knowing the facts before you make the decision. (IMHO) In this case, the Lions know Best wants to play. They agree to PUP, agree to a 1yr thorough health screening during the bye week. This way, the NFL, the Detroit Lions, and Jahvid Best were fully knowledgable of the situation.
Maybe I'm rambling for nothing, way off base, and Best never plays another down... I just hope that we see #44 next monday night.