Time-weighted control charts allow detection of relatively small shifts from the target value. Time-weighted control charts tend to go out of control sooner than I-MR, Xbar-R, or Xbar-S charts when the mean of the process shifts slightly. For example, suppose that a milled part has to fit precisely with a different part, and the milling process is already in control. You can use a time-weighted control chart to detect small shifts in the process.
Time-weighted control charts can be used with individual observations or data in subgroups.