It depends on what you want to achieve. There is saveWithFullMetadata which is the "full save". It saves ID, location and data. Then there is saveWithId, which is just the ID and the data. Use this if you want to restore the BlockEntity at a different location. All of those can later be used to call BlockEntity.loadStatic to create the BlockEntity again.
There is also saveWithoutMetadata, which you can use to save just the data. Use that if you create the BlockEntity yourself somehow, you can then call BlockEntity#load to restore the data.