Hi,
The only way formatting a drive normally would be unhealthy would be by formatting it several times a week for a year or two, that might bad on the hd.
Formatting an older drive can be rough too.
With a fairly new healthy drive, the normal "only when necessary" formatting should not be harmful. Annually or semi-annual should be fine.
I have an old hp pavillion with ME installed. I basically use it for coding and surfing the net. I have formatted it maybe 2-3 times a year for the last 3 years and have not noticed any issues yet.
