Probably not 100% necessary but certainly desirable/good practice. Will put strain on the internal baffles if pressure unequal between chambers.
Have seen some new 3 chamber boats with only 2 prvís - eg F-Ribs.
If youíre going to the bother/expense of speccing prvís then one for each chamber in my opinion - our boat has 5 chambers and 5 prvís.
Just be prepared to top up pressure more regularly as they will leach air.