If you buy a package and have to cancel (within cancellations guidelines/penalties, etc.) you have only paid a $200 deposit and you just get it back and your done with them.
If you book room only to start, you will put down the price of one night as a deposit, which of course you would also get back if cancel in guidelines which are closer to the date. But then, if you had purchased tickets somewhere else, you now have those tickets for a future date. So the initial output is larger.
However, the package has to be paid a month or so in advance, so its all being paid then. Where room only is when you get there.
Just depends on what you want to do. I usually just package it up from the beginning. A lot of times when Im making reservations I buy the tickets with the package at a certain price, and then Disney raises their ticket prices at some point and then Im locked in at the lower price. So, if your certain your getting them through Disney and not elsewhere, Id just do it now before any price increases can occur.