Fullwidth characters take up more horizontal space than standard Latin letters — originally designed to visually align with Chinese, Japanese, and Korean characters, which are naturally wider. This tool applies that same width to any text.
In CJK (Chinese, Japanese, Korean) typesetting, mixing narrow Latin letters with wide native characters looks visually uneven. Unicode's fullwidth block gives Latin letters and digits a matching width, so text lines up cleanly in that context.
Outside of CJK typesetting, the extra spacing gives fullwidth text a distinctive stretched-out look that's become popular purely for its aesthetic, unrelated to its original technical purpose.
Unlike some decorative styles, fullwidth covers the entire Latin alphabet, digits, and even spaces, so nothing gets left unstyled.
Each character is rendered at a fixed wide width by design, originally to visually match Chinese, Japanese, and Korean characters — that's also what gives it its distinctive spaced-out look.
Closely related — the Aesthetic generator on this site adds extra spacing between fullwidth characters for an even more pronounced stretched-out look.
Generally yes, though its extra width means it can take up more of a character limit than the same text in normal letters.