Candle wax also enables them to burn longer, without being messy, at least at reasonable temperatures. If it's too warm the wax will melt but it's OK at room temperatures. Wax may also help with water-proofing the cotton (although in my experience enough additive to proof against water also makes it hard to light - this applies to Vaseline too).

I tend to carry them in first-aid kits, for wound-cleaning.