The Demons deck is fairly straightforward, a combat-focused monstrosity making ample use of Belakors Warstorm Surge effect
Its activated ability probably wont come up much in 1-vs-1 Magic, but in Commander
Its a huge payoff in dredge decks, and it was banned in Modern in 2019 to try to stop the Hogaak, Arisen Necropolis decks from destroying the meta
Even though the humble Negate may seem like a better exchange of mana-to-possible-counter, remember that opponents are often tapping out to cast their huge Fireball and not expecting to see a Spell Pierce countering their spell as well as a Counterspell would, anyway
During the design for the Mirrodin block, Rosewater wanted to make use of +1/+1 counters in a similar way to the spikes while also making artifact creatures matter
Impulse gets you through your deck quickly, allows you to quickly search for an answer to an impending problem, and does it all so effectively that almost any blue deck capable of running Impulse in any given environment has done so without hesitation