All the answers are correct

(Funny coz I'm listening to "I never Shall Forget" by Paul Morton & I think , if I heard properly, the singers end in what sounds like a sus4 to me

)
Sus chords really sound nice individually- even better when used in the "right places" (like any chord i guess!)
Under13 said they are used to resolve. An example of that is when you are ending a song [5-1]
in C major:
5: G/F-A-B-D [GM9 or 5maj9]
1: C/F-G-C [Csus4] [over here you feel the "pull" towards a 1 major chord, but I normally like to defy that pull & sustain that chord instead

]
the pull would be towards something like this:
1: C/E-G-(B)-C
But as the other guys said- you will find that they fit nicely in other places as well.
I like the sus2 when playing the 4th note in a scale [say in a 1-4-5]
still in C:
1: C/F-A-C-E [FM7 or FM7/ C in bass= 4 chord/1 bass]
#4: F#/E-G#-A#-C [Passing- optional- F#9b5]
4: F/C-E-G [Fsus9 (which is really a 1 chord with a 4 bass)]
#4: F#/G#-C-E [Passing- optional]
5: G/F-A-D [Dm/G]
[Ok, I'll have to hear that, I'm just imagining the sound, so excuse errors.]
help, is this [ F#/G#-C-E] a G#aug with F# bass or Caug with F# bass?