Limbo on interception missions can have a Cataclysm up that spans at least two points, keeping all enemies in stasis. Other Examples where negative power strength can be beneficial: Her damage multiplier on affected targets is NOT affected by power strength, making both viable depending on the mission needed. Most famous example: We all know that a Nova built for positive power strength (Slova) is useful for the massive slow and AoE damage, whilst the negative power strength (Speedva) is great for making enemies come to you faster.
With that I don't mean "use Overextended on Chaos Nyx", as the ability is unaffected by power strength. I am curious as the what abilities can benefit from negative power strength that scale with power strength.