Is walking still beneficial to a "runner"

If someone is healthy and is trained and has the endurance to run, I don't see how choosing to walk would provide any benefit. If you generally like walking and it makes you feel good mentally go for it. Or if you are burned out from running and looking for a very low intensity workout, that's fine to walk as well. Sometimes it isn't feasible to run because you aren't dressed appropriately and so on. But other than that, if you have the choice between running or walking, I think running is a much better use of your time. Walking beats sitting though.

Activity is good in any form. Running everyday can be hard on the body. The body also gets used to a workout, so changing it up sometimes is good. Walking is not just for the unfit people. You don't have to workout at full tilt all the time.

First of all, you have to define "workout". Then you have to define "benefits".

If the goal is to just burn calories, then the answer is "yes, you will get benefits from walking because you will burn a few more calories than you would have sitting in a chair".

If the goal is to improve or maintain fitness, then the answer is "maybe". It depends on your fitness level. If the intensity stimulus of an exercise does not meet a certain threshold (e.g. 50% of VO2 max), then you will not get much in the way of "fitness" benefits--that is, you will not increase your cardiovascular fitness level by doing the activity.

A trained runner who runs at 7-8 mph will not get any fitness benefits from walking 3 mph.

There are also general health benefits that accrue from being active, but those are mostly in comparison with a sedentary individual.

As to your last statement--just randomly changing activities is not going to provide fitness benefits unless the intensity is within your training range. Unless you run really, really slow and can walk really, really fast and are on a hilly course, if you are in a "rut" from running, leisurely walking is not going to help.

Now walking on an incline or on a treadmill with an incline feature is a different story. That can be a very helpful alternate workout--but that's only because you can set the workload to be in the same training intensity range (or close to it) as your usual exercise. The same could be said for cycling, rowing, stairclimbing--as long as you can work at the lower end of your training range.

Are people posting their responses based on opinion, personal experience, or scientific material? In a book I just finished "The Lure of Running" it seemed to imply too much walking isn't beneficial to running and you might as well jog.

All three.

Not beneficial how? It's not going to give you the adaptations that running would, but it certainly allows you to recover faster, especially for someone that isn't fit enough to run every day.

So if I run 45 miles a week and feel good, is there any reason I should choose to walk over run on any given day?

I run 6 days a week and walk for 90 mins on Sundays pulling my daughter in her wagon. I'm sure there are a lot of other reasons runners chose to walk too.

What benefit do you get? You get the benefit of recovery. You get increased blood flow to the muscles used when running which helps to repair the micro-tears in the tissue. Also, if you walk fast enough, you get your heart rate into the fat burning range at the very least. It's really not that hard to get into that range.

So you can't get these benefits by running slow?

It's not either/or. It's not binary. Sometimes I run. Sometimes I walk. I run for 30-40 minutes. Sometimes I walk for an hour or two. Sometimes I ride the bike. Sometimes...