Some things are forbidden via halacha in local terms, such as eating, but some things are so forbidden that we may not derive hana'ah, benefit from them in any way. Chameitz She'avar alav HaPesach, leaven that we retainined in our possession over Passover, is such a category -- in fact, this site says that one may not even return chameitz items purchased on Pesach for a refund as that constitutes benefit.
Benefit, though, confuses. me. I know from learning parts of Masechet Sukkah (Schottenstein 31b2, note 19, referencing R"H 28a), that one does not derive benefit simply by fulfilling a mitzvah (that is, the status of having been mekayem the mitzvah is not inherently benefit), so I assume that one's burning the leftover chameitz, though he might gain spiritually by being yotzei an obligation, is not "hana'ah". Daf 35a(3) note 24 references Masechet Shabbat 25a-b which says that one may derive more physical and practical benefit from the burning of T'rumah which has become tamei, like using the fire as fuel in an oven. But I do not see that there is a blanket issur of hana'ah for said T'rumah.
Where there is such a law, like by forbidden chameitz, can one derive similar secondary benefit through the destruction of the leaven? Does fulfilling the obligation to burn it and then using the flame to create warmth in a house, or run an oven in which other food is cooked, or to dry clothes etc. constitute a forbidden benefit in the same way that a direct benefit (reselling it, feeding it to one's animals etc.) does?
