Toxic Miles
As you probably know from How Often To Run and Supercompensation, I do not believe short, easy runs are generally beneficial. There is a place for Recovery Runs, but only when you are recovering from Delayed Onset Muscle Soreness or injury.
Contents
1 Toxic Miles
I believe that if a run is too short to build endurance, to slow to build aerobic or anaerobic capacity, not hilly enough to build eccentric resistance, then it is toxic. These Toxic Miles do nothing but slow up the recovery from our quality runs, which reduces the intensity we can do these quality runs and make us more injury prone. Some people call these 'junk miles' as they are worthless. I prefer the stronger term, 'Toxic Miles', because I believe that they have a negative impact on our training. You can be a successful runner while putting in a lot of Toxic Miles, but they make success much harder to achieve.
2 Cross Training
While the stress of Toxic Miles generally degrades training results, cross training between quality running days can produce benefits. See FIRST.
3 Counterpoints
There are arguments against the 'Toxic Miles' philosophy.
3.1 Clearing the Head
As Michael M points out, running does bring mental benefits. Not 'mental toughness' so much as a time of peace, freedom, and meditation.
3.2 Calorie Burn
The benefit of extra running for weight loss is less clear. The extra calorie burn is likely to be fairly small, but the exercise may improve the muscle's sensitivity to insulin. See Nutrient Timing. Doing cross training may be more beneficial however.
3.3 Base Miles to Support Quality
There is a belief that to perform quality training, you need a base of slower miles. While I can see the value in building up distance before embarking on speedwork, I have found no evidence to support the idea that doing slow running between speedwork sessions is useful.
