Starwood has long been known as a smaller chain but with one of the single most rewarding loyalty programs. Uniquely they allow points transfers at a 1:1 rate to most of their partner airlines, of which there are more than 30. Problem is United is one of the very few that doesn't give you a good rate.
About the only good place to transfer points from is the Chase Ultimate Rewards program to United, otherwise transferring points on United is not worth it. Starwood points have the power to transfer to almost any airline you could want at a very favorable 1:1 ratio. So for every Starwood point you own, that equals 1 miles on most airlines. There are a few notable exceptions, of which United is one of the very few.
United's transfer rate is 2:1 and in a world where you can choose to fly with someone else, why use such an unfavorable transfer rate? In the past, I bought miles flat out to make up the difference on a United flight, rather than transfer Starpoints at such a terrible rate.
If you use miles often like me, then using them efficiently and getting the best bang for you buck is always the option you want to look for. United's offering is half the value of almost every other option when it comes to transfer partners at Starwood. 50% value is bad for almost any situation, it would be a better idea to transfer to American Airlines, Delta, Alaska, or any other international partner before using United.
So why United, why do you value your miles so much higher than everyone else? I don't understand it, and I avoid United partly because of this poor transfer rate. I'd like to see United change this, but I won't hold my breath. In the mean time, I suggest looking for other options.