Flexibility is a benefit.
Temporary workers can determine their availability.
The downside is job security. Typically, the organization which is seeking temporary help pays the employment agency to find qualified candidates for them. Employment agencies often offer medical benefits, paid time-off, 401K retirement plans, and pay increases. Be sure to ask about this as agencies differ in what they offer you. Agencies and search firms can assist with relocation and access to large companies who outsource their recruitment function.