For example, you could run a deck dense with evoke creatures, cast them for their low evoke costs for early value, then get them back later via Colfenor triggers to use again
Boros already has this sort of effect attached to a legendary creature you can run in the command zone with Zirda, the Dawnwaker, but its nice to get another one in Gruul with Agatha of the Vile Cauldron
With Abyss Proxy Shop, you can play with The Monarch Token and every legendary Commander staple you need all without spending a fortune
It also keeps your opponent guessing as to your plans, or allows you to shift (pun intended) your plans on the fly to deal with your opponents current position
It's also more difficult to pin down a set booster's rarity ratio, with each slot in the pack having its own chance of being a different rarity
Secondly, in decks with a way to sacrifice a lot of cards for value before bringing them back for another go around