So it might not be practical most of the time, but this DOES stack. That means you can play two of them to stop a predicted "Advance, Advance, Score" (e.g. on a suspected IAA'd 4/2) or three of them to cancel the Corp's clicks entirely (at the cost of most or all of your own though, so outside of specific situations mostly involving extra Runner clicks it's not worth it)
This aside, you can also stop a predicted fast advance with just one copy which can be game-changing if you can snipe the prospective Agenda from HQ and/or the game is currently tied up at 6/6 and you need another turn to try and squeeze a point out of somewhere. Populist Rally can give you confidence that they won't score out next turn, and combined with any Event recursion you can create a Clot style effect that locks out fast advance but without the option to purge.
Or you could just run this alongside Clot to prevent them from purging it! Either option is fine, although this by itself is much more limited against FA but costs no influence in return. If you generally just find yourself needing to squeeze out one or two more turns against FA and can't spare the influence for Clot, it can be very valuable.
Finally, it makes it harder for the Corp to flatline you using something like SEA/Scorch/Scorch. For 2 creds and a click, you can stop worrying about that until next turn. This can give you time to win, find protection, hit HQ with an Imp to get the SEA Source out of there, or even just let you make a run this turn without fear of death (since next turn you can simply not run in order to avoid SEA Source)
Essentially, denying the corp a click denies them options which might have been very painful for you. It's relatively versatile and hedges out some very bad outcomes, offering you a sense of security in whatever else you're doing this turn.