I wrote it to help a user who needed to generate date strings with GMT time zone, and then send them to a web service.
This can be done by calling DateTime.SetTimeZoneOffset(0), however it will have other unwanted side effects.
the problem is associated with using SetTimeZone in long running apps that run over a daylight saving change event - I'll leave you to read the above links but note that this issue has arisen for others in the forums - although I suspect some did not fully comprehend what was happening (my situation until fairly recently).