KST has been a total game changer for me commissioning plants and machines.
SCADA systems and HMIs are generally not set up to poll data from PLCs faster than 1 Hz.
Using a driver for the PLC communications protocol I write all of the variables of interest to a CSV file at 10 Hz.
PLC scan times are usually 10-100Hz so while I can't capture everything the PLC sees or higher frequency components to the signals than the PLC can measure, it is happy middle ground between a proper DAQ and just using the HMI software.
In addition a DAQ wouldn't be connected to all of the PLC IO but with this system I can easily grab all the PLC tags I want, as well as internal PLC tags that are not IO points.
Most HMI software has pretty brutal plotting capabilities as well (Citect process analyst being the only one that is better than passable), so on top of getting at least 10x the resolution in the data I get to use KST which is great for zooming and panning on the plots, creating sets of plots, or different plots for specific tests.
Not all HMI software even allows plot configurations to be saved, so you can spend a lot of time just re-adding the time series to the plot and setting the scales.
The plots are used for commissioning reports and records.
Bokeh is a nice kit as far as it goes, but I hit scaling problems quite early with it - as I understood it, it was supposed to send incremental updates to the client, but in fact it resent everything every time - and therefore fell over after half an hour when the time to update exceeded the update rate. Maybe I was holding it wrong.
[0] https://kst-plot.kde.org/