My two cents and advice:
I've seen recurrent posts on WUS where people post pics of watches on their wrists seeking opinions on whether their watches are too big/small.
To these posters, I think it's important to remember that people here collect watches for various reasons. Some buy to wear, whilst some buy to build a collection. Some do both. Therefore, opinions given often depends on the replier's proclivities and their priorities in collecting. I'm approaching this from a purely functional and aesthetic (dare I say fashion design) perspective.
I've often thought that whilst wrist size is a valid barometer of whether a watch fits or not, it's equally important to factor in one's body size, and the size of one's hands in relation to one's watches. A large watch (in relation to wrist size) can make an overly large hand look smaller and proportionate. The converse is true too. The colour of the dial, and shape of the case & lugs has a similar effect. White will look bigger; black, smaller as a general rule.
In addition, I've also seen large watches on small to average size wrists where the watch just looks right when the man has been tall, muscular or large framed. My buddy is 6'3" with the same size wrist as mine. However, my 46mm Breitling looks better on him than on me, if I'm brutally honest.
Furthermore, aside from these ergonomic considerations, lifestyle factors can influence whether a watch is too big/small and how often it's worn. I just sold my car and bought a scoot living in inner city Melbourne. Consequently, I rarely wear my Breitling (the largest watch I own) purely because it's too big to fit comfortably under my motorcycle gloves.
The good news is it prompted me to buy two of my grails - a Speedy and Rolex Explorer ll, which fits perfectly on my wrist and under my motorcycle gloves.