Im sure its a stupid question.. but.. Why do some jet boats have cavi plates and others dont? Other than hull makers.. Is there a big performance difference?

Cav plates can completely change the attitude of the hull like B-Rad says, on the river boat we used them a lot like brakes, you dig into some down pedal to suck the hull down in the water both slowing it down and keeping the hull from taking flight when you hit a roller, it also allows you to stay in the throttle to improve steering while under a hard maneuver.

I would put plates on everything I own if I could.

Now something like Bennetts on the other hand have even more versatility, they can adjust individually and adjust out the attitude of the ride and correct a listing problem because your big ass cousin can't seem to stop eating all the damn BBQ.

GT 

So the jets that have no plate at all are gonna be squirrely at high speeds?

Not necessarily.....This question sounds loaded to me  

They technically have a "drag effect" most of the time, the hull will normally have rocker (corrected at 10:02PM) or some other feature making them squirrely to start with, if that makes sense...The plates are to "mellow" their effects....

My dads Crusader and my Carrera both have Bennetts on them.....The little boats have ride plates  

GT