Vtec definitely won’t hurt your engine. Like Maximuz said it helps with power and fuel economy.
On this website, about 3/4 of the way down the page, it explains the Fit engine very well and more importantly in relatively simple terms.
The Truly Amazing Honda Fit/Jazz
Also, I'm almost positive the Fit is always in vtec at freeway speeds, it helps you keep it in 5th gear when accelerating or climbing a hill, thus saving fuel.