1. difference is between using freeze/thaw vs using store/retrieve in the Storable module.

   freeze/thaw write-to & read-from scalars. Ie, in memory. store/retrieve write-to & read-from files.

   Obviously, in order for the frozen data to persist beyond the program run, you would need to write it to persistant storage anyway.

2. are either of these useful for writing incrementally?

   That kind of depends on the nature of the data you are storing; and/or how you choose to use them.

   You could store your data to a file periodically, each time writing everything you have so far and overwriting the same file each time.

   Or, if the data you wish to save becomes complete in discrete chunks, then you could save each chunk to disk as it becomes complete. But you would need to write each chunk to a separate file as storable disk files are written and read as complete entities;

   It is possible to use freeze/thaw to write multiple storable chunks to a single file and then thaw them back, but it requires you to do the file handling yourself, including adding extra code to delimit the individual chunks.

More information about the nature and quantity of the data might yield better answers.