If your large ship is fast enough - and Cutters often fall into this category, Chaff CAN be helpful if you need to put some distance between yourself and whoever is shooting at you.
Sorry, Corvette, but you're more Federal Chevette when it comes to raw thruster speed.
But as stated, large ships do suffer from Large Ship Syndrome - small ships can pull right up on you, and all that chaff jitter becomes meaningless. I also make use of this fact myself when fighting against large NPC's, because they can spam chaff endlessly, and do - which is why chaff dispensers become a primary target for me. I just love shooting those little things off their hulls - then half their tactics are elminiated, and if they happen to stop to reboot, it's rammin' time!
Point Defense... it seems useful on every single ship, except the Type-10. I've tried positioning a PD or even two in multiple locations, but... they generally don't seem to be all that effective. I've started using both PD and ECM on my combat Type-10 with much better results, but the ECM is still a little weird to use.
ECM is a waste, point defence does same job and works against things that aren't locked onto you too. I love it when my pd shots down a NPC missile in flight that was aimed at my target. I'm like "oh no ya don't, he's mine!"