I agree with the above comments. Heart rate monitor and calorie counters (sometimes not exactly accurate) may be beneficial to some. Also, water-proof and extra battery life could be an asset depending on training.
In general, advanced GPS functions or wireless connectivity options would be unecessary options for me personally. Also, I do not want to wear a watch that looks like a caculator or cell phone with a strap attached to my wrist...too bulky and complicated, so the simple workout features are fine.
I personally do not use the heart rate monitor anymore, it is good data, but for me, it feels uncomfortable to wear.
I use laps, distance, time, current pace the most. I would like to be able to program advanced workouts, however (currently I carry a piece of paper so I don't forget anything and it is quite unconvenient).
5k: 20:12 (December 31st 2012)
10k : 44:30 (November 6th 2011, March 18th 2012)
Half Marathon: 1:35:27 (February 3rd 2013)
I like half marathons! Seven completed so far and trying to get back on optimal shape to improve my PB. Once I complete my 10h half I will start thinking about full marathons.