Tested it now, and from what I can gather:
The value is completely ignored if you turn off smoothing in-game.
If smoothing is on in-game, then:
0 - No smoothing
1 - No smoothing
2 - Some smoothing
3 - More smoothing
Higher values seem to revert to either 1 or 2.
Lower framerates equal more smoothing, so most likely these values are how many frames the movement is smoothed over.