I'd vote no contract of work. I am where I am today because my jobs never stick to a list of duties - I get to see technologies outside of my job, meet people outside my department, I get to learn soft skills that my job doesn't demand. One of the most valuable career skills has been making myself available when the demand comes for someone to do something different, and holding to a job list cuts off that option.

Without it, I wouldn't have ever touched SQL back in 1996, I'd still be an RPG developer in my little niche on AS400, I probably wouldn't be a DBA today and loving what I do.