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
Other cards such as Unown [M], Cleffa, and Cool Porygon helped on support, and Murkrow was used as a backup attacker, taking advantage of the massive strength Darkness Energy cards provided at the time
UPDATE 9/15/16: Ditto
Any deck trying to squeeze some extra utility or even combo potential out of its land base can do worse than to run a copy, and certain decks like Cloudpost or Amulet Titan have made it look broken by circumventing its primary drawback: entering play tapped
(You cant choose an Energy card that was discarded by this Ability)
Kismet In the early days of Magic , most prison effects were symmetrical, and this makes it a little challenging to abuse them effectively