What are the two most important advantages of helical gears

What are the two most important advantages of helical gears over spur gears of the same pitch size and the same tooth width?

Solution

Silent operation: In a helical gear train, the teeth engage a little at a time rather than the entire face at once. This causes less noisy power transfer in case of helical gears. Non-parallel shaft: Helical gears can be used for transferring power between non parallel shafts. Though you have to compromise on efficiency in this case. Strength: For same tooth size (module) and equivalent width, helical gears can handle more load than spur gears because the helical gear tooth is effectively larger since it is diagonally positioned.