I'd second much of what is discussed here as has been my experience as well...
How the monitor will be used will most likely determine if it will experience burn-in. If it's going to be used to display a non-moving image (such as a restaurant menu near a cash register), that could potentially burn-in after a few years of being left on all day. If your computer screen is going to be left on all day while you use it, and perhaps you're worried the desktop wallpaper will get burned in, most likely not since 1) you'll probably be using it much of the day 2) it will probably go to sleep after a few minutes or hours of inactivity anyways when you walk away unless you force it to stay on longer.
When I have experienced burn-in, it was for a static public display monitor (similar to the restaurant example) where the same image is left on day and night, for months (and years) at a time.
I have also worked with offices that do not turn on screen savers or power save mode because that would slow down the workflow during the day. I really haven't seen any burn in with those scenarios. Instead, what I've been seeing a lot in the past five years is LED screens (both monitors and TVs) going "purple" because the plastic layer between the backlight and screen is chemically breaking down and instead of being transparent or white, is shifting the backlight to a purple color.
Also, I have heard if you leave an LCD screen that has burn in on bright white for a few days solid, it can clear out the burn-in to some degree, although I haven't tried this.
TL;DR: Regular use I wouldn't worry about it. Leaving it on a non-changing image for months 24/7, possible, but even then not guaranteed.