When I am working up loads I use them to place a close to charge on the scale and then use the dipper to add or subtract powder.
I also use them occasionally, mostly for pistols, when I want to throw a few rounds together with no serious intent. For instance to use up a few odd left over bullets. I used to use them a lot more, when I played around with reduced load cast bullets more. Actually they weren't Lee dippers, I made a set of my own. I developed my load, then made a dipper to hold the charge I wanted.
Lee dippers never hold the charge that the chart says they do, it is always lighter than claimed, for the lawyers. When used right they can produce charges almost as consistent as a measure, but you can't depend on the chart to tell you what that charge will weigh.