Over means the bettor is anticipating a lot of action and this is how bookmakers get to them. If you have been watching and betting for a long time however, you may be able to objective and exercise restraint and not be overly excited over a match and only bet on the under side. Anyway, under is not always the correct answer as it really depends on the match, the teams, the gameplay and many other factors but most beginners end up getting too excited and betting mostly on over without proper analysation.
I have bet on over 0.5 before in a Seria A league in Brazil but I lost the match. It was an accumulatikn with over 10 odds in total. All the mat he's has been played that day and I won all expect this one which was tomorrow. I would not have taken it if I knew it would be played tomorrow and that was no cash out on the betting site as if the time because it was many years ago. No goal was in the match and I lost it. I later checked the team that is playing to know that one if the team which is the dominant one do not use to score much and it is hard to score the team also.
But sometimes people choose over with a proper analysis but then match will disappoint.