Stimhack is a major tool for every faction. Especially Anarch and Shaper.
First and foremost, for any faction, being able to take 9 creds out of thin air and make a run with it, will allow you to get that agenda or make that last run in a pinch. At 1 influence and 0 creds, it is a cheap price to pay only 1 brain damage for it. This as saved (and won) the game for countless runners. The 9 credits can be used to trash an high cost asset in a pinch.
For Anarch, it allow them to install bin breakers (Paperclip, Black Orchestra, MKUltra) for much cheaper, since you'll have 9 credits to do so, on top of using those credits for the run.
For Shaper, it speeds up their setup immensely. Put a Self-Modifying Code on the board, make a run with Stimhack, and install whatever program with the 9 credits you just got out of nowhere. The economy boost is amazing.
Stimhack give you the most tempo out of any tools in the game. 0 creds, makes you run, give you 9 creds, all for a tiny one brain damage. Well worth the price. And with a cost of 1 influence, you'll see this card be splashed everywhere. Stimhack is the most powerful event card in the game, in my opinion. There is no substitute that gives you the same tempo.