How are you macroing the mouse click to place the plant?The reason it's good is that it's very easily macroable, it runs about 75s for a level buying potato seeds.
You can macro the process pretty easily where it only requires a key press.
I've had a hard time finding any other on demand labor process that can be as easily macro'd.
Cows are by far one of the best labor dumping methods, both for ease of upkeep and profitability, but potato's are great for semi-afk or fully-afk labor dumping.