I think the main purpose of solfeggio is to give you a way to think about the way notes relate to each other within a key. If you don't want to deal with the silly do-re-mi syllables -- and who does, really? -- it makes a little more sense to use numbers that correspond to the steps of the scale. Do is 1, re is 2, mi is 3, etc. It's much, much more useful than just thinking about the letter names of the notes, not least because it lets you instantly transpose any riff or chord progression to any key.
"When I play, I express my feelings very fast." -Yomo Toro