Pros:

• Truly amazing technology... the fact that you could play on your keyboard and it would write everything out is incredible.
• Has a library to keep everything organised.. because, well, musos are not the most organised people.
• The collaborative nature is awesome, really makes it useful for entire bands to work on.

Cons:

• $50 a year is kind of pricey for a budding musician, or for every single member of a band to cough up... but thems the breaks I guess.