I took advantage of the great weather yesterday to enjoy a leisurely ride on the back roads of Williamson County. My companion on this lovely afternoon does not like to stand to pedal and in our 34 mile sojourn, standing was not required. Thus I return to a topic posted sometime last year, because she is not the only cyclist with whom I ride who eschews standing until absolutely necessary, ie. she runs out of gears and still needs power to remain in motion.
Another repeat: the disclaimer of not being an expert; but I am experienced. If you fall into the category of Non-Stander, then resolve to put this device into your repetoire. Here are some tips to help you get started.
Don't worry about the bike (frame) going side-to-side with each pedal stroke. However, keep the tires (handlebars) straight. We can't have you wandering all over the road. When you come to a moderate climb that is easily taken seated by one smaller gear, instead to go one larger gear and stand for three sets of eight strokes. This should not require more power and actually might be less, and definitely a slower cadence. What you are looking for is whatever gear you can comfortably pedal. If you generally run 75-80 rpm, you might find 60 rpm or less is what feels best to you.
On an average ride, try to be out of the saddle at least every 15 minutes. Let me rephrase that: Don't go more than 15 minutes without standing to pedal.
The main benefit is change of position, giving your back a break and using different muscles. The longer the ride (like 3 or 4 hours), the more your seated muscles need relief. Secondarily, should you come to a steep climb actually requiring power-strokes, you won't be calling on muscles that are not properly stretched and warm.
One other thing about starting with 3 sets of 8 reps, standing. That is only 24 reps and about 25 seconds. You should be aiming for two minutes or more.