Youre not trying to look threatening right off the batinstead, youre quietly building your gameplan, getting cost reducers or draw engines on the field, and laying the groundwork for a big swing later
To make Secret Lair drops that much more enticing for fans, they dont only include whats being sold
Many of the best also have a rather low casting cost, allowing them to hit the battlefield early and start generating value
If you do, draw X cards, then you may put a permanent card with mana value X or less from your hand onto the battlefield, where X is the sacrificed creature's mana value
This goes doubly so in Commander where your 100 card deck is full of singletons, meaning you're even less likely to draw each card you put inside of it than in other formats