Drop ins were a way of giving a look of builtins without a lot of expensive reworking of kitchens or buying custom cabinets for a cooktop and oven. Whether it was the drop in like the Mark 27 or the set on like the Modern Maid, it gave a new look to a kitchen. When Frigidaire came out with the Flair, they ran an ad with an early 50s range replaced by a Flair on its modern base cabinet and the difference it made in the kitchen was amazing. There were performance sacrifices with many of these ranges, but they offered modern looks when people wanted them.