Pixels are tiny squares, so a diagonal line or curved letter would look like a jagged staircase. Anti-aliasing fixes this by adding soft, partially-colored pixels along edges to fake a smooth line.
When you want it
Almost always for text, logos and shapes on screen — it makes them look crisp and professional.
When to turn it off
- Pixel art, where hard edges are the style.
- When you'll later scale with nearest-neighbor interpolation.
Gotcha for transparency
Anti-aliased edges are semi-transparent, so they only look clean over the background they were designed for. Putting an anti-aliased PNG cutout on a different color can reveal a faint fringe — relevant when you remove a background or work with transparent formats.