That card is a complete house if you no longer have to pay mana to keep it around
Not that you ever will, but thats how gambling works
No chance you're paying six mana for a meager +3/+3
With powerful white enchantments like Smothering Tithe or artifacts like Sword of Feast and Famine, being able to find one at instant speed is crucial
Each booster contains at least seven special alternate-frame cards, four or five rares or mythics, and at least eleven premium foils
Apart from the issue of some cards not having playable substitutes, the other reason I tend to dislike this advice is that part of what makes formats like Commander fun is the diversity that they offer, and this diversity is built, in part, on players being able to access and play with weird, old, nostalgic cards that don't really see play in other formats