Physical access to a computer is complete access, in terms of security. Therefore, this cannot be used for most computations. Latency is also an issue. A lot of computations can locally be done more cheaply and efficiently if two long journeys must take place with each unit of work at a distance. Ergo, this is likely to be viable only for "public" computations like Bitcoin mining or Folding at home. Public computations usually are poorly funded. Therefore, this business plan is unlikely to succeed without some vast innovation in terms of distributed computing reaching the masses. Example: Intelligent job scheduling ala Google Omega and beyond.