Onhwy61, good question.
For me, it is to know what time it is. For my job, during the week I have to know what time it is all the time. Certain things have to be done at or by a certain time during the day or they cannot be done that day (or ever). And I could get myself in a world of hurt by having my watch/clock set back 15mins and me being caught by that. That's why I have a clock on each one of the four computer monitors I have on my desk (and there are several clocks on the wall, one on my cellphone, and my office phone, and...) and I check my watch for accuracy against them on a regular basis.
On the weekends I often do not where a watch because I do not care to know the time or to think I have to know the time. My idea of a vacation is to not wear a watch or use an alarm clock for an extended period.
Is there also something else going on? Of course. Fashion. Desire. Conspicuous consumption. And to some extent, what Jla noted above - some people simply admire the technology which goes into a good mechanical watch.
