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 : 42:30 (March 9th 2014)
Half Marathon: 1:35:27 (February 3rd 2013)
After completing my 10th HM it's marathon time. To be totally honest now it's recovery time due to an ankle injury, THEN I'll think about the Marathon.