Certain 3 to 5 decoders only decode specific inputs due to design choices that prioritize certain output combinations while categorizing other states as "don't care." This approach allows for a more efficient design process by focusing on unique input combinations to generate required outputs. Multiple valid designs exist, such as using Y1 = I1 AND I0 to avoid conflicts. In applications where every input must be decoded, these shortcuts would not be applicable. The EN signal functions as an ENABLE line, further influencing the decoder's operation.