For a poolroom owner/manager, the advantages of drop pockets are that they are quieter, less wear on the balls, less maintenance and hassle issues keeping the ball returns cleaned and unobstructed and the need to keep the ball collection box cleaned. As a player, I feel the sound of the ball hitting the bottom of the pocket is more aesthetically pleasing. Also for older players, bending and reaching down to retrieve the balls out of the ball return collection box can be a little difficult.
The main advantage of ball returns are that it's easier for players to gather and rack the balls at the end of every game, particularly for those practicing by themselves, and ball returns eliminate the need to keep the pocket bottoms cleaned out.
In my opinion, once players learn the accepted proper etiquette that the player who will be breaking the next game retrieves the balls from the two sides and two corners at the head (breaking end) of the table while the racker retrieves the balls from the two corner pockets at the foot (rack end) of the table, it really is not an issue or delay to be playing on a drop pocket table.