Wheel width & offset aspect - consider the offsets and widths of your car wheel and the wheel you try to fit. The differences in them will have to be factored in along with the adapter thickness.
Stud clearance aspect - the stud length and the adapter thickness determine protrusion of the stud over the surface of the adapter, i.e. if the stud is 1.5" long and the adapter is 1.25" thick, the stud will protrude 0.25". If such case existed, the mounting pad of the wheel must have deep enough pocket to accommodate the stud protrusion.
Brake clearance aspect - this is probably self explanatory. Consider both radial and lateral clearances.
Cost effectiveness aspect - adapters are not exactly cheap. Finding a properly-sized set of wheels are not difficult nowadays. Unless you are hell bent on fitting something like a set of Ferrari wheels on a VW, the adapters are likely to be cost ineffective.
All those said, I've considered fitting a set of Corvette wheels onto my Boss 302, made the Status Grinder on the Solstice to have dual PCD so they can fit the PCD of the Z06 & CTS-V also looked at Saab, Saturn, Malibu, Catera whels for Solstice winter set, tried to run effectively-zero offset on the 350Z, used 300ZX, RX7, GS300, & other wheels on my previous DSM, and basically played with numerous fitting scenarios with all my cars.