Vantaggi
The only downside is that ultimately, as a contractor you are living and dying but the contracts you can get. I was part of a rather large contract, that the GOV ended. Not a big surprise, but watching my unicorn die in font of me was sad. Best company ever, IMHO. I miss working for them and hope the opportunity arrises where I can come back.
Svantaggi
Just what's listed above. I also "have to enter at least 5 words", so enjoy that last sentence.