One of the characteristics about modern chess is the fluidity of material values. When Morphy and Andersson were ruling the roost, sacrifices were common, but they were often with a clear tactical goal in mind - get the opponent's king stuck in the center, remove a defender, etc. They were less often made in a more positional and long-term sense.
Looking at the games of the top players these days, it seems like exchange sacrifices are extremely common for such positional compensation. The opponent's rooks don't have great open files, while the other side's minor piece has a nice square. These aren't sacrifices that immediately finish the game, but they demonstrate a willingless to bend the age-old rules that a rook is worth 5 points and that bishops and knights are worth 3.
Here are two examples that caught my eye when I played through them, both from Corus (Wijk aan Zee) in the same variation of the Queen's Indian Defense. The first one is lightly annotated, the second isn't annotated at all.
Playing through games like these helped me feel more comfortable sacrificing the exchange for long-term play. While the following game I recently played in Mallorca isn't from the same opening, it does share some characteristics with the above games.
Question 1: What would you play here after 16.Bxf5?
Question 2: What would you play here after 25.Ne1?
Question 3: What would you play here after 30.Kb2?
Here's the entire game in one viewer: