One advantage is similar to the advantage of using replenished developer.
Due to the fact that you re-use the baths over and over, you don't have to concern yourself with wasting developer as a result of your developing tank requiring a far greater volume than the amount of developer used up by developing each 4x5 or 5x7 or 8x10 or ??? sheet.
Due to the fact that you re-use the baths over and over, you don't have to concern yourself with wasting developer as a result of your developing tank requiring a far greater volume than the amount of developer used up by developing each 4x5 or 5x7 or 8x10 or ??? sheet.