First off, let's start with Benjamin Franklin's "What good is a newborn baby?" quote, when asked what good electricity could ever do. Primary research leads to unknown and unknowable benefits, because it is impossible to know what will come of it.
As an example, let's consider the magnetic moment of the proton. It's a rather esoteric measurement. The proton acts as a tiny magnet, and some researchers wanted to know exactly how strong of a magnet. So, they set up a strong magnetic field and looked to see how the proton behaved. They ended up finding two different values.
As it turned out, those two different values were the result of electrons getting in the way of the measurement. As it turned out, there were two different chemical environments in the molecule being studied, and that caused the two different values. The chemists loved it, because then they could directly measure the electron density.
Then the doctors realized that the chemists had an awesome tool. They could use it to measure the concentration of water inside a patient's body. Bam, MRI.
All this from esoteric primary research.