Tangential to your point, but is there any particular reason a Dyson sphere must "radiate away in a predictable way" (like the black body you described)? Surel

Tangential to your point, but is there any particular reason a Dyson sphere must "radiate away in a predictable way" (like the black body you described)? Surely a civilization sufficiently advanced as to create a Dyson sphere might either (a) direct excess energy in a beam to some satellite civilization or (b) store excess energy as matter, rather than just jettison it into space?