Using a Params block gives compile-time checking against attribute typos. One
might inadvertently set myLLSD["autofill"] = false and only discover it when
things behave strangely at runtime; but trying to set myParams.autofill will
produce a compile error.
However, it's excellent that the same LLProcess::create() method can accept
either LLProcess::Params or a properly-constructed LLSD block.