The purpose of a watch is to tell time. A mechanical watch has been doing that for centuries. However, from a 'purpose' base approach, technology has made mechanical watches obsolete. From a practical point of view, technology has made electronic watches more accurate with much more possible applications for a given size.
Why there are still mechanical watch around is purely due to its artistic beauty. People tend to romanticized mechanical watches due to abstract reasoning while disregarding its true effectiveness. I can understand why. It is nice to appreciate something pretty.
A number of people have asked me this question, “What would be the most useful complication on a mechanical watch today?” This is an easy question to answer. For me, it is the GMT function (some called it UTC; conceptually there are differences but operationally they work the same i.e. tracking another time zone).
Writing about watches is a hobby of mine. Not a lot of my readers know this but my daily job and career is totally different. It involves the world of finance. Travelling to the four corners of the Earth is a normal occurrence for me. If I am not travelling, I would be engaged in teleconferencing with global clients. This set of circumstances require me to have a watch (if it is mechanical) that can track global time zones so that I would know when would be the best time to make conference calls.
Wouldn’t a Worldtime watch be more appropriate? Yes, it could if it has the location of all my clients. Due to the lack of space on a dial, it is close to impossible to note every possible location on Earth onto the Worldtime watch. Also, if a country suddenly decides to move to another time zone, the dial of any Worldtime watch prior to the change would be erroneous. Case in point: the change by North Korea by 30 minutes last year to move the country from GMT+9 hours to GMT+8.5 hours. I don’t think any major brand has ever put Pyongyang as a Worldtime reference before but the fact that you need to relate to a city to get the time zone is a step too far. A simpler process would just remember the reference time zone plus (+) or minus (-) GMT and refer directly from there.
Daylight Saving Time used in the summer months for certain jurisdiction also plays havoc to a Worldtime watch. Typical way to denote such jurisdiction is to colour such cities differently from the rest. Furthermore, as it is now, a dial on a typical Worldtime watch is too busy for my liking.
What would be most efficient is a fourth hand; a GMT hand that moves one round of a dial in 24 hours. There should also be 24 hour scale for reference.
I usually fixed the GMT hand to point towards GMT time. Now, you just need to take note of the target location time zone reference to the GMT. For example, if you know North Korea is 8.5 hours plus GMT, you just refer the GMT hand and add 8.5 hours to give you the time in Pyongyang. If Los Angeles is 8 hours minus GMT, you just refer the GMT hand and minus 8 hours to give you the time for the US West Coast.
As a travelling watch, you don’t it to be too big or too obvious. Something around the 43 mm range would be sufficient. It should also have a sporty nature to it in case you want to take a dip in the hotel pool. In short, it shouldn’t be too dainty or too expensive or made out of precious metals (don’t want to provide the necessary temptation to the unscrupulous when travelling). Nevertheless, it should have a pedigree that exudes style, quality and class.
In my collection of Western watches, I got the following GMTs: (Left)
Schroeder Joailliers 1877 GMT; (Right)
OCEAN7 LM5 GMT.
Up to this moment, I own two Tissot watches. Both I bought when I visited Switzerland back in 2011; the Tissot Gents T-Classic Le Locle (see: http://westernwatch.blogspot.com/2013/10/tissot-gents-t-classic-le-locle.html) and the Tissot Seastar II (see: http://westernwatch.blogspot.com/2014/02/tissot-seastar-ii-t55848311-refine.html). Before and since that purchase I have not looked at another Tissot because of the many issues relating to the brand from counterfeit all the way to the lack of serial numbers (Google it to find out more). 
