If you are like me, running is when you think of all the things you need to think about. I think about and plan just about all of my lessons for my classes during my runs or biking sessions. I also tend to pick apart all my previous races and plan how I want all my future races to go. I choose, re choose, and choose again the different races I want to do. I also will set up a full day's menu during a run sometimes or plan out a week's worth of meals if it is a longer run. I do have to focus on the run sometimes though.
If the workout calls for it, I am completely in the run itself. Watching the clock, my pacing, where I have gotten to by a certain time, all these are mitigating factors during certain workouts.
This goes back to my run yesterday. It is important to vary what you are doing for a run and what you want out of it. The basic 45 minute run I do where I lace up, go, and think about what I want to do that afternoon is as important to me and my family as the timed tempo run that I nail splits within a 5 second range for 5 miles consecutively.
Unless you are an elite runner, mix up what you do and what you want, even if you are in the middle of a training plan/program with a very specific goal. It will help the well rounded you.
I run this way and have for a couple years now. Last November, I ran my first marathon on a repeated mile course (not an ideal situation for a strong time) and finished in 3:28:43. I am pretty proud to say that was my time and I utilize a wide range of paces, intensities, and types of workouts in my running life. I am a lot less structured that most people. A month and a half before that I ran my first half marathon on a very hilly course and ran a 1:34 without a watch or mile markers, totally by feel. I will tell you there were a lot of triathletes on the course that day with their Garmin watches on and I enjoyed sipping my Gatorade while watching them finish.
I am not bragging here, because lots of people are faster than me, but I will say, something works that I am doing and I really feel it is my wide range of paces and intensities. If you keep it fresh, training ruts, boredom, and bad days are easier to move past.
Try it. List some different things you are going to try for one 2 week training cycle and give it a go. Do a couple easy jogs with no watch, do a tempo run, a long run, do some mile repeats fast with significant breaks in between, and hill repeats. See how the stretch of time felt?