ESD SPI/ISP bus protection
The NUP4114 has very low capacitance, in the 0.3pf range. It also shows that the NUP4114 working on differential lines at 500Mhz. Since SPI, I2C and Uarts don't operate at this speed, it's safe to say that the NUP4114 would not affect signals under 100MHz and would be fine for what you described.  

The GPIO capacitance of most microprocessors is much higher, usually 10x higher, so I wouldn't worry about adding this part to digital lines of low speed (under 50MHz).