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There is no need, but it is always beneficial:

Reciting Darood Sharief before and after any dua is a powerful means for the acceptence of that dua. It is reported from Allaamah Shaami that Allaama Abu Ishaaq Ash-Shaatibi has mentioned:

Trans: Durood Sharief is definitely accepted by Allah Ta’ala. It is unlikely that Allah, The Most Generous will accept one part of dua and reject the other.

Allaamah Abu Sulaymaan Duraani says that dua wherein Darood Sharief is recited before and after it is unlikely that Allah Ta’ala will accept the first and last part of the dua and reject the middle portion.

(Shaami-Vol.1) Source: http://www.khanqah.org/books/p/84/salaatul-haajaat