Why are time zones necessary

A time zone is a region of the Earth that has adopted the same standard time (local time).

-Most adjacent time zones are one hour apart (although a few are 30 minutes).

-They compute their local time as an offset from Greenwich mean time (GMT).

As earth rotates, the different countries or different part of the earth are at daytime and nighttime. Since they have different daylight and nighttime times, we would need time zones.