Do many mathematicians write a lot (including expository articles)? Or are there a fair majority of mathematicians that just write papers and don't bother with expository material? Which is better? Do mathematicians lose out if they do not write expository material?

closed as off topic by Andrew Stacey, José FigueroaO'Farrill, Harry Gindi, Martin Brandenburg, Charles Siegel Aug 5 '10 at 12:23
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G. H. Hardy recommended that young mathematicians spend time on research, and when they are older and less adroit at research they should write books (to pass on the knowledge they have amassed). Probably in mathematics departments at top research universities, those who write primarily expository material will be at a disadvantage in salaries and promotions. On the other hand, mathematicians who write primarily exposition can find perfectly good positions at other types of institutions. For example: William Dunham, author of four wellreceived expository books, is Truman Koehler Professor of Mathematics at Muhlenberg College, Allentown, Pennsylvania. 

