I use a 5 meter to one set of amps and a 7 meter run to another set for exactly the reason you suggest, that I'm able i isolate my equipment from standing waves and vibrations which would effect my source components if i located them near the amps/speakers. I'm also able to make adjustments from very close to the listening position. If your preamps can drive long runs of cable its a great way to go. I think the reason you don't see more of this is both ergonomics (i.e. WAF) and cost. You usually have to special order these lenghts and may not get return priveleges - so you really have to do some homework before you commit.
Who uses long interconnect like in dealers?
Ideal setup has front end components close to listening chair and run long interconnect between pre and power where power amp sits in between speakers; I have seen many high end dealers to adopt this setup and result is usually more than great. This way front end components do not obstruct speaker imaging and can also avoid bass heavy (vibration) location. But if that is ideal, why do I rarely see long interconnect for sale in used market? I don't think people only upgrade components and short interconnects?