What role does the initial consonant play in a Hangul syllable block?

In the Hangul writing system, symbols are organized into square blocks to represent syllables. The initial consonant serves as the first element of each block.12

If a syllable begins with a vowel rather than a consonant, a small circle is used as a "zero initial" to maintain the structure of the block. Following this initial element, the block includes a vowel nucleus—which may be simple or complex—and an optional final consonant or consonant cluster at the bottom, known as patch'im.12