Interesting question J.S.Matthew. There is a saying I've heard that goes, "jack of all trades, master of none." As Lucidwarrior says, a jack of all trades is someone who should have a wide breadth of knowledge and ability. A good place where you can find jack of all trades is in the world of diplomacy.
While diplomats will tend to have a particular area of specialization, the demands of the career also require them to at least be a jack of all trades. Especially for countries with limited resources, their diplomatic missions overseas in some places will have a limited staff complement. This sometimes means that an officer and/or staff in an Embassy sometimes find themselves dealing with issues involving economic matters, political/security issues, cultural affairs, etc. As for limits, well this is good only to the point where they can initiate an understanding or commitment to cooperate or work on a particular area of interest. When it comes to working out the technical details, the entry of specialists and technical experts are usually required and brought into the process.