Arduino Pro Micro LED pins
The Pro Micro wastes the B0 and D5 pins of the MCU for two onboard LEDs indicating TX/RX communication.
For many projects, two more pins seem much more useful than this LED feature, so you can desolder the resistors of those LEDs (or solder directly to the resistors without removing them).
While the Atmega32u4 MCU features 26 GPIO pins, the Pro Micro itself makes only 18 of them easily accessible. If this is a limiting factor in your keyboard or other DIY electronic project, you can buy a microcontroller with more pins (like the Teensy, Proton C, Elite C etc.), but for much more money.
Another options is to grab your soldering iron and make two more pins available desoldering the LED resistors.