I don't blame you; they are quite awesome.
The "slow" feature was awesome for two main reasons: (1) you could slow down records and get double-speed, high-pitched plays, (2) you could (obviously) pull a Kevin McCallister and slow down plays to get half-speed, low-pitched stuff, (3) you could switch between the two at will without stopping the tape, and (4) you could slow down records and plays to get more space on the tape at the expense of quality (also, since it most likely pushes less power to the motor, it is probably better on battery life!).