If you were playing other creatures, Steel Golem gave you a good one but it could also cripple you if they could block or otherwise stop it without removing it, and there were several good ways to do that
One mana tricks tend to be pretty nice in aggressive decks, as you get some serious tempo when you use them to win combat, and this one definitely gives you enough of a boost to be worth running in those decks
This, again, means that spells cost one mana less for each creature you have on the board.
In the case of Ugins Conjurant, youre looking at a free dies trigger, a free cast trigger, and maybe an extremely unlikely place for a tribal Spirits build to dump a whole bunch of mana
Conclusion In recent years, players have focused on the overall gameplay experience rather than building highly optimized and competitive decks