Natural sunlight helps to regulate circadian rhythms. Your body's hormone for sleep, melatonin, reacts to light and levels change according to time of day. Spending too much time indoors can create sluggish patterns of hormone production and sitting outside in the yard can help reset these rhythms for better sleep at night.
Vitamin D has been on everyone's health radar recently and with good reason. It is produced by sunlight, though, and more effective in this natural form than a supplement. Being outdoors in natural light for 15 minutes a day can help your body manufacture its minimum requirement of this essential vitamin.
Eyes also seem to get better in natural light. Artificial lighting and in particular heavy computer use can cause eye strain and nearsightedness. These fake lights are also being linked to headaches, neck and back pain and migraines. Getting outside and just looking at your yard, a treeline or cloud cover can relax eye muscles. Evolution gave us the ability to scan for predators or prey against varying backdrops. Looking at objects seems like little work but in reality it's a workout for the eye muscle.
Even if you don't have a large yard to sit in, or if your patio is tiny, you can still set up a nook for breakfast or afternoon reading with minimal work. Set up a few plants or paint that shed so your eyes have something to gaze at and absorb some vitamin D. Keep in mind that most devices these days are mobile and will work outside in the yard as easily as indoors or an office. Plus it's healthier for you.
Additionally designers are taking new looks at small space living and a small patio is the perfect place to try out some gadgets. Think a Murphy style bar that folds up against the wall when not in use. Or folding chairs and furniture that can be put away into a wall-hung closet. There are even plastic all weather storage containers for gardening equipment that can double as a table for out door dining.
No matter what your yard size or condition, there's no real excuse to stay inside if the weather allows it. Being in the yard is a homeowners treat and should be taken full advantage of. If you can get outdoors each day for a short time, do it. If not for the fun of it alone, then do it for your health.