I was amazed at how simple it was to use. Pretty full-featured, as well.
A friend of mine was responsible for scoring system on games. As they had some real awards (like bikes, tickets etc.) they captured the entire flow of the game with various statistics and later analyzed them for weird variations. That was in Flash and people used browser plugins to slow down the play, that was easy to spot. Of course it won't stop 100% of attacks, but it raises a bar sufficiently to thwart most attempts.
Great for debugging or just inspecting/reversing/hacking in general.
Im glad if similar tools are being made available as browser extensions, it might lower the barrier to entry and get more people poking at the network layer.
PS: https://github.com/square/PonyDebugger is a cool debugger that lets you use Chrome developer tools when developing iOS apps.
PS2: https://paw.cloud/ and some other tools take these proxies to a whole new level in terms of UI/polish.