why is GMT time so important?

GMT, or Coordinated Universal Time (from WWV) is an international standard for all time calculations.

Many years ago, the village of Grenwich Englad was choosen as the reference point for all time.
The Earth is divided into 24 equal time zones, making it a relatively simple matter to convert time from GMT to local time.

For an individual computer that is not on a global network, it realy doesn't matter.
However, if you are on a large multi-time zone network, the specific time is very important.
If you need to sort events or entries by time posted, using GMT for the time stamp makes it a much easier task than having 24 different 12 Noon's to place into proper order.

Chas

I'll chime in with an additional answer based on practicality - if you were going to use a local time for the stamp, you'd have to add additional information to indicate what time zone the time is in (e.g. 08:00 EST rather than just 02:00). That's an extra 24 bytes per record.

Jay