The ability to specify a Format String for each index in the Array to Spreadsheet String would let individually saved data columns have different numbers of digits of precision or significant digits.
I use the Array to Spreadsheet String to save 2D column data consisting of Time (X) and one or more Data (Y) columns. Sometimes the columns have different inherent resolutions yet the Format String needs to be set to allow the largest number of digits for all columns. This can result in :
If nothing else, it saves on file size. The Array to Spreadsheet String function could check whether an array of Format Strings was wired into it or not to decide what to do (make it polymorphic). Thus existing code could still be used.