Is this that old idea that is new again? Google Microsoft DFS and see. The problems are such that anyone that wanted to do this would just do it. Those that can't deal with it, won't.
Perhaps you recall the Startrek show that featured aliens called 'The Borg'. Each alien member on the spaceship was connected to a network in a way that their brains combined to make something superpowered.
Let's say you have a small LAN of 50-100 PC workstations and each of these PC's has a 1TB SATA hard disk. Let's also assume that users only use about 25% of that 1TB disk for applications and data on the local PC. So a 100 PC LAN has 75TB of unused disk space.
Is there any software that would allow one to take unused disk space from each PC and add that capacity to a pool of storage space? It would seem you could even use striping and mirroring of data over multiple PC's for performance and reliability.
In other words, could each PC contribute unused storage space to a big pool that a designated server could treat as one big storage space, as in a storage area network?