I can think of one possible reason not to convert - some laptops cannot use
the hibernate or save-to-disk facility if the primary partition is anything
other than FAT16. You should check with the manufacturer if you use this
facility.

You will get between 10% and 20% more usable space on C. As there is ample
room on D to create a full backup, then you can easily cover the small risk
of something going wrong.
--
Jeff Richards
MS MVP W95/W98

my laptop for whatever reason came with 2 'local discs' comprising the
total internal storage capacity. disc 'C' has the system software
installed on it ,is 2GB in capacity and is in the FAT 16 format. disc 'D' is
in FAT 32, 10GB space, and is basically empty right now. everyhting i've
read suggests that i should convert the 'C' disc to FAT 32. is there any
reason not to do this? can i damage anything?