I, personally, try to take my dog for his walk at least every other day. I try to make it every day when the weather is nice. Walking your dog regularly has several benefits:
The dog gets exercise as does the owner. Regular exercise is also a known stress fighter a brisk walk in which you build up a sweat is better than a slow lazy one. We want our dogs to have strong hearts and muscles.
The dog is able to not stay "cooped up" this will make you dog more manageable as it won't be so restless (especially if your walks are of a fairly brisk nature.) Tiring out our dogs makes them happy AND manageable.
A dog is not designed to lay about all day (neither are we.) regular activity helps keep the joints properly functioning which will help combat joint damage (such as osteo arthritis) later in life.
Also, your dog might get the chance to socialize with other dogs and this helps build its confidence and friendliness.
I'm sure there are many other reasons but I'm sure that you get the picture, regular exercise is good.
So, I'd recommend at least walking your dog 3 or more times per week, every day if possible. You'll both be better off for it.