I loved Ben’s sus chord video. It was the best treatment of sus chords I have seen.
Julian, I am no expert, but sus chords are my bread and butter in certain keys and song types. 2 chords are great as a base chord and 4 chords are great transitional chords. When doing many song types in D, I’ll go drop D and use the Dsus2 as the root chord. Allison Kraus and US, and some other “newer” grass groups live off them (it’s just a guess, but I suspect AKUS uses D2 more than a straight D). Dsus2 has a darker and more complex sound than D. In fact, if you don’t get an F# in the mix, I think it can work with a minor scale as well. In alot of the praise music that I do, if it’s in A, I’ll use the open A, B and E as drones while I double the melody and harmony on the D and G string. It sounds rich and is typically easy to do. When playing in G, I often use G5, C2 (some call it a C9) and D2 as my 1, 4, 5. You can also pick out the melody and harmony on the G and B string while droning on the D and E strings (which would be working around a D2). In Bluegrass, if the song hops quickly from G to C and back, I’ll use the C2 form, as the fingering is much easier. In short, they are just something to add to your quiver. They can give a more rich or dark sound than standard major chords, they can serve as a transition, and sometimes, they are easier to do in quick transitions.
Here’s an example of a song chock full of sus chords. It’s got D2, Asus4 and 2, C2 (or 9) etc. and if you try playing it with the straight major chords, it just doesn’t sound right: