100% of the time that I am at work. A good, accurate Seiko.
I need to know what time it is, right now, with precision, and I can't use a cellphone.
And I still wear one about 90% of the time when I am not at work. A quick glance and flick of my wrist, vs. reaching and pulling out a cell phone.
I'll take off my watch and wedding ring to do dangerous/dirty tasks, but then it's right back on.
My oldest never saw much need for the watch that I bought her as a present - a titanium Seiko. Now, in her 3rd year of medical school, she realizes how critical that watch is. Her hands are often dirty, wearing gloves, or full with medical equipment, patient's hands, etc. and she cannot pull out her cell phone...but a quick flick of her wrist and she can see what time it is...very important in her profession.
Only a watch works in her profession...and she wears her Seiko every day now...