I start with the ITA matrix when I have a pretty complex itinerary, trying various combinations that interest me. ITA has glitches, but if you are persistent you can make it work. After I find something reasonable, I look it up on google flights, which helps me decide where I should book different flights. For example I was able to between three continents, five different countries in the summer for less than $1000 + 30,000 miles. (I used miles for one segment only that would have been the most expensive.)