It’s best to use it. Your system will sound better if you don’t make speakers do what they’re not designed to do.
A 3 1/2” speaker isn’t going to reproduce bass and will only distort. Ok, it will do alright at low volumes, but not when you crank it up. There isn’t any reason to send bass to it to begin with.
If you have an amp that limits the bass frequencies to the dash speakers, then the capacitor isn’t necessary.