Pros
Health insurance is offered by Adecco, taking a temp position at Google offers an opportunity to "get your foot in the door", Adecco is responsive to questions about insurance, sick days, etc. when they come up, TVCs get access to free food and snacks onsite at Google and very cheap GBUS rides
Cons
Adecco takes a large share of the contract payment for your onsite contract at Google, contract negotiation is difficult (or impossible?), healthcare is offered, but very expensive, (virtually) no PTO, only 3 days of sick leave per year, no 401k or other benefits offered, the promise of "getting your foot in the door" at Google does not guarantee conversion to full time employment at Google (in some cases, coming on as a TVC makes it harder), often TVCs work on more than what their contract states, but because of legal concern about co-employment liability, Googlers take credit for TVC work, working on-site at Google does not include many benefits afforded to Google employees (team off-sites, Grow classes, healthcare, retirement benefits, etc)