I use filters and EQ to do a variety of things...

1. To balance the sound (EQ)

2. For vocal effects - Hi Pass

3. To separate a mono instrument for a stereo effect (For instance a Guitar - I will hi-pass the left channel, and low pass the right).

WRT to what John said, while an EQ is designed to "equalize" the frequencies, I do not ever use it for that, as a flat sound is generally unpleasant. Balancing the sound means putting the highs and lows at a level that works with the song, not just flat.

Clip envelopes can also help tame plosives and other mouth sounds. As can, sometimes, zooming in and muting (with the K tool) a very short range of samples.

Note that you can split the clip on either side of the problem sound, and apply any corrective EQ, etc, to only that clip using its fx bin.