With time zones, if it’s 10am where you are and you need to talk to someone somewhere else in the world, you look up their time zone and see what time it is there, and you know if it’s 3pm that they are probably still at work, and if it’s 1am there then they are sleeping, and so on.
If you don’t have time zones and you just know it’s also 10am there, what do you look up to quickly know whether they are likely working, eating, sleeping in that location? Do you look up when sunset is in that city and then check its latitude and the time of year so you can estimate where they probably are in their day?
With time zones, if it’s 10am where you are and you need to talk to someone somewhere else in the world, you look up their time zone and see what time it is there, and you know if it’s 3pm that they are probably still at work, and if it’s 1am there then they are sleeping, and so on.
If you don’t have time zones and you just know it’s also 10am there, what do you look up to quickly know whether they are likely working, eating, sleeping in that location? Do you look up when sunset is in that city and then check its latitude and the time of year so you can estimate where they probably are in their day?