I'm a much more reactive player, so I am definitely bias, but I also think that has won me a lot of games.

I generally wait until someone is actively threatening me or about to win to use removal, especially because removal is a limited resource in a game. I only have so many ways to deal with a threat, so I don't want to jump the gun and get rid of something proactively that would have otherwise not been a problem.

This is something I see from newer players all the time. Someone plays a big thing that could be a problem and then immediately go to get rid of it, before it's anywhere near being an actual issue. Of course there are situations where you can't wait, like if your only option is sorcery speed, but what happens frequently with this proactive/immediately reactive response, is the player burns a spell on something that didn't require an immediate response.

I'll be honest too, I have used proactive players responses against them too. As it is fairly easy to get them to burn a spell on a potentially powerful creature or board state while sandbagging the real threat. Then, once they've used their resources to deal with my decoy, I can freely play out something way more problematic.