The main difference between select option and ranges is that ranges implicitly or automatically creates internal table with fields like OPTION,LOW,HIGH,SIGN,etc . Where as in case of select option we have to explicitly create internal table.
When you declares a select options it will implicitly declare an internal table (ranges) for you.
While using RANGES syntax u can declare internal table explicitly.
The only need of declaring ranges is when you are not taking input from the user but you want make limit based selection at that time it will be use full e.g.
SELECT ** from ** where MATNR in val_range .