What "exactly" does a filter envelope do?

[Remedial]

Okay, I know, in general terms, it contains the same ADSR envelope as the amp envelope and the, rather than affecting the volume, it's effect is on the cutoff point of the filter. So, tell me if I'm right here, but, theoretically, the attack phase determines when the filter takes effect (whether it be at the start of the note or later on in it's cycle). The decay phase is the amount of time it takes for the cutoff to get to it's sustain point (which I'm guessing is the cutoff point that was dialed in using the filter cutoff knob) and the release phase is how long it takes for the filter to stop having an effect on the sound (i.e., the unfiltered sound shines through). Am I getting this right? And, now, the filter envelope amount would be how much the filter cutoff is actually affected by the dialed in filter envelope settings, right? So, at it's full amount, the sound will adhere to the filter envelope settings to a tee? I've been trying to figure this out for a while, but I haven't found any guide that "truly" explains the usage or purpose of the filter envelope, even the Sound on Sound synth series. Let me get your inputs.