What are the advantages and limitations for historians in drawing on the writings of foreign observers?

Writings of foreign observers is good to get new insights of different cultures, however it may ignore or mislead important aspects of the studied events.

Explanation:

Pros

It is helpful to see different insights about different events and cultures. Sometimes  when studying, for example, historical events in which the observer belongs to the same country, it is possible to bias the research and lead to incomplete conclusions. That bias is not likely to happening when a foreigner observer is doing the job because he/she is not influenced by local culture.

Cons

This is the counterweight of the previous advantage. It is true a foreign observer may be more impartial, but it is also true that if the observer is not very aware of the manners and culture of the civilization he/she is studying, then lack of information and incomplete conclusions may be stated.  It is necessary a balance between an impartial analysis and a well knowledge of culture of interest.