One of the many advantages of HPLC is that it is easy to automate. You can create an injection sequence, run it overnight, and have your data ready for review in the morning.
Contrast this with an assay by titration, for example. Often this is done manually, with not only valuable analyst time being spent but also the possibility of human error introduced.
In this sense, HPLC assays are less prone to error and therefore more reliable, accurate and precise.