This is often done in preparation to sell the former church building to another party.
In this context, Profane does not refer to swearing, but rather to the older definition of those things that take place outside the temple.
The Diocesan Bishop (or Archbishop) will issue a decree stating that the church building has been relegated to profane use.
This has the effect of deconsecrating the church building.
The diocese will sell the building for any use as long as it is not sordid.