No other Magic creature can populate the board as efficiently and early as the Sergeant
What's not to like about an enchantment that can stop attackers, save your blockers, make your creatures invulnerable to removal, give you free morphing, and allow recursion of comes-into-play abilities -- for free
You get to put +1/+1 counters and draw cards equal to the number of permanent types of cards in your graveyard when Korvold deals combat damage to a player
In the earlier years of the game, a 3/3 with Flying and Vigilance was an offensive and defensive powerhouse
The idea was of course that while neither side would really be playable on it's own, being able to decide in game whether you wanted a land or spell was well worth the slight downgrade on rate
Either way, youre adding spells to your hand that your opponents cant interact with until you go to cast it