Quite a lot of work went into making the SD card life as long as possible.
The data partition is therefore a different format to maximise the life of the card, the emonSD image is designed for use with emonCMS - if you want a multiuse image, install emoncms with the emonScripts but leave out the partition part of the setup.
However, you run the risk of the card failing early.
As I said, there is a modification such that the data partition will be limited to10GB in future.