You can use them with certain fares on AF/KL.

ETA:

http://www.delta.com/content/www/en_...tificates.html

KLM

• Valid on all flights coded as KLM and operated by KLM.
• One-way upgrade from published Economy fared in Y, B, or M class to Business Class.

Air France

• Valid on most transatlantic flights operated by Air France.¹
• One-way upgrade from Economy when booked in Y, B, or M class to Premium Voyageur Class.
  or
• One-way upgrade from Premium Voyageur when booked in S or W class to Business Class.

¹ Not valid on AF operated 747 aircraft flights; only valid on flights with the Premium Economy Cabin.