Same thing with tidal height curves - I used to do it religiously for anchorages, crossing bars etc, and felt very pleased to know the depth to a decimal. Trouble is it is nearly always "wrong". For example tonight at 2100 the depth outside the lock was predicted to be 6.0m, falling. It was actually 4.5m, so a yacht may not have made it in time for the last lock (1.5m max on the cill)

Now I tend to use twelfths and leave a good margin, even though the Avonmouth curve is quite asymmetric. The streams here are also high, and directions and rates vary a lot over short distances, so it is pointless trying to do accurate calcs IMO. I work on a rough calc for spring or neap rates for passage planning, and directions to compass points.

On saying that, I think it is good to know the theory and be able to "do it by the book", but you need to know when it is appropriate to use - and that is something that learning by rote won't help with.