The great advantage of a parametric equalizer is that it allows the user to change the frequency and Q. However, this is offset by the fact that this very ability complicates the inexperienced user's efficacious use the system. Adjustments can be so complex that the needed change might be difficult to determine.
A parametric equalizer uses knobs for its control functions, which makes it more difficult to visualize the set-up of the equalizer. Even so, it admirably performs the main functions of an equalizer which is to control the loss and gain in a frequency within a sound system.
Parametric equalizers usually have 3 to 6 bands. Some have overlapping frequency ranges. Others have broadband control which allows it to be used over the complete frequency range. Most parametric equalizers have a switchable range switch that allows operation in a x1 or x10 mode, allowing the frequency to be equalized on an even finer scale.
Found in almost every venue, the parametric equalizer certainly has its advocates, but it has by no means replaced the graphic equalizer as the preferred device for sound technicians.