What is the purpose of this simple 1 capacitor 2 resistor high pass filter?
What is the purpose of this simple 1 capacitor 2 resistor [high] pass
  filter?


The extra resistor gives you an extra degree of freedom.

For the standard RC high-pass filter in the first schematic, the transfer function is

$$H(j\omega) = \frac{j\omega R_1C}{1 + j\omega R_1C} $$

So, the asymptotic high frequency gain is 1 and the corner frequency is \$f_c=\frac{1}{2\pi R_1 C}\$.

But what if you want something different than 1 for the high frequency gain?  Add another resistor.

It's straightforward to show that, for the second schematic, the transfer function is

$$H(j \omega) = \frac{R_2}{R_S}\frac{j \omega R_SC}{1 + j \omega R_SC}$$

where

$$R_S = R_1 + R_2$$

So, you still have the high-pass filter but now, the asymptotic high frequency gain is \$\frac{R_2}{R_S}\$ and the corner frequency is \$f_c=\frac{1}{2\pi R_S C}\$.