When I was a kid and just getting into electronics, I needed some wire, and my dad was cheap so he bought me a small spool of speaker wire. I used it on my projects for years before I bought myself some nicer stuff.
The insulation, generally speaking, isn't very good. If it's left in the sun for a few days it tends to get sticky and starts degrading VERY quickly. It also doesn't tolerate heat very well at all, when it gets warm, it also gets sticky. That being said, it works very well for low voltage (I've used it for 3.3v, 5v, and 12v) stuff under a few (let's say 3-5) amps, that won't have any UV or heat exposure.