Standard PD Laser and LR PD Laser? PD Laser is okay. Not great, and inferior to Vulcan, but if the ship cannot use ballistics, then PD Laser is useful enough. LR PD Laser is a flux-efficient, all-purpose weapon - part PD, part long-range zapper akin to Tactical Laser. Not great at any single role, but useful enough if you need LR PD to do more than PD, especially if you do not have IPDAI for Tactical Laser. (IPDAI is one of those rare hullmods that require Tri-Tachyon commission or lucky station salvage.)
Ever since LR PD Laser got its flux cost lowered from 100 to 40, LR PD Laser has become a very useful filler weapon. I often use it instead of Tactical Laser (partly because PD and LR PD are fairly common, and other lasers are rarer).