It depends on what you fly. If you fly online almost all the time, and usually under ATC guidance you might want to update it more often, as arrivals and routes change. However if you just fly on your own you should be ok with the release. The difference is the accuracy and contents of the data. The Navigraph data includes Approaches, SID/STAR data, airways, and nav fixes. The default x-plane data is user maintained as opposed to the navigraph stuff which presumably get their data directly from the major providers. X-Plane's data does not include approaches or SID/STAR data. Another important thing to note is that the default data is for the entire native x-plane world, and the Navigraph data will only work for the three devices that currently use it in X-Plane (UFMC/EADT's new GPS and the CRJ) No other planes will be able to use the data.