The main selling points is to run an AmigaOs like OS on cheap PowerPC (Apple hardware).
It is a hobby. Some people prefer to build the ultimate DOS box for playing DOS games and demos on real hardware or go nuts and play with expensive japanese computers (NEC 9801, X68000 or FM Towns).
To build on a similar comment to this effect, I have four Apple-built PowerPC machines. In order of acquisition:
* 1 eMac (G4 processor, Radeon graphics): $40-worth of labor
* 1 PowerBook G4: $80-worth of labor
* 1 Power Mac G5 (single processor): free (was being thrown out)
* 1 XServe G5 (dual processor): free (was being thrown out)
Meanwhile, you can buy quite a bit of Apple's PowerPC hardware in working condition for anywhere between $25 and $200+ on eBay. Many of them will come with either OS X Tiger or a botched OS X Leopard (which I've found to be notoriously unusable on most PowerPC Macs). I personally run OpenBSD on my own such machines (I'd dabbled with GNU/Linux previously, but there were significant stability issues, particularly with hardware support; while OpenBSD's hardware support isn't that much better, at least it's more-or-less consistent across targets, so when graphics enhancements arrive on one platform (for example), they'll typically hit my PowerPC boxen, too (which is precisely what happened with 5.5 when OpenBSD adopted a DRI implementation)).
What are its main selling points?