I'd say it depends on the set. That's usually a pretty valid strategy, but every once in a while, a really good edh card gets spoiled and just starts trending up. In those situations, it's often cheaper to buy early. Still, it can be hard to know if a card will spike or not sometimes. I would say if it's good in standard, probably wait. If it's good in something like modern, and unlikely to get banned, then the price will often just stay high.