It's useful to bear in mind that only a handful of cable manufacturers actually make their own wire, or even assemble their own cable products. Most of the wire is purchased from a small number of suppliers, and many of the cables are now assembled in China or SE Asia. (I realize that some companies, such as Alpha-Core, Kimber, and others, manufacture their products in the US.) Hence, there seems little reason to worry about "mixing and matching" cables with different brands. The sole issue, it seems to me, is performance -- as others above have noted.
Having said that, if you find a brand that seems to perform particularly well in your system -- maybe due to some fortuitous combination of electrical characteristics that have a synergy with your electrical components and speakers -- you might want to stick with one brand. I have recently spent quite a bit of time playing with speaker cables and interconnects, and found that Alpha-Core Goertz speaker cables (MI2 copper) and interconnects (TQ2) work better in my system that any other brand I have tried, so I decided to stick with this brand for most of the important connections.
Having said that, if you find a brand that seems to perform particularly well in your system -- maybe due to some fortuitous combination of electrical characteristics that have a synergy with your electrical components and speakers -- you might want to stick with one brand. I have recently spent quite a bit of time playing with speaker cables and interconnects, and found that Alpha-Core Goertz speaker cables (MI2 copper) and interconnects (TQ2) work better in my system that any other brand I have tried, so I decided to stick with this brand for most of the important connections.