​THE ADVANTAGE OF ADAPTING METHANOL INJECTION SYSTEM

boost up the octane rating
Octane rating is the measure of a fuel's ability to resist knocking. The higher it is, the less your engine knocks. Super grade gasoline is 98 RON, while racing fuel has a  octane number as high as 116 RON. 
Mix the 122 RON methanol with high grade gasoline can create an equivalent to racing fuel, but more convenient in practice. If you fill up your tank with racing fuel, you burn it and consume your money all the time. But if you fill the methanol in a separated tank and only use it when you need it, you can get what you want in a much more sensible way, obviously.

cool down at highest efficiency
There are many ways to lower the intake temperature, for example use an intercooler or a methanol injection system, which is especially important for a turbocharged engine. When you upgrade your car with a larger turbocharger, the stock intercooler won't be enough. Now you're in a dilemma: you want to exchange it with a larger intercooler, but are hesitate for the foreseeable turbo lag, due to the longer fill-up time.  
On the contrary, methanol injection system don't have such drawbacks. It's direct; it's fast; and it even cools down the intake air while easing the turbo lag in the same time.