NeoICSerial and SPI on the Uno - pin 10
The "Unusable 10" is explained in AltSoftSerial library


  The "Unusable PWM" pins can be used normally, with digitalRead() or
  digitalWrite(), but their PWM function controlled by analogWrite()
  will not work properly, because AltSoftSerial uses the timer which
  controls that pin's PWM feature.




Pin 10 on Uno is SPI slave select if the Uno is SPI slave (then it is an INPUT). 

If the Uno is SPI master, this pin must be set as OUTPUT. For this reason it is usual to use pin 10 as slave select for the (first) SPI slave. SPI shields have this pin hardwired as slave select for the (first) SPI device on the shield.