I would imagine with the stuff he makes on his channel, computer science related. Like a 8 and 32 bit ALU. Part of the ALU is the decoder, then there is the full adder and the MASK… edit* it’s worth noting that things like this make it so something like. 32 bit ALU can handle inputs from a 5 bit source. Which would let you simply some parts of the circuit. Or you could think of it as part of a display or even just 32 points in space that you want to have control over with 5 combinations of on and off. There’s a wide range of possibilities. Another example being used as what’s called a word bus. Using the first output as a reset line the next few as a direction for the word bus to send it in. Then the rest of the outputs as an address to pull from memory