We don’t use favicon.ico because the .ico format is uncompressed ~ 16 kB. Instead we suggest creating a compressed favicon that works in place of favicon.ico for all web browsers we tried. These files are typically 1..2 kB instead of 16 kB, which is significant for a text-based website.
favicon.png favicon-16x16.png favicon-32x32.png
Then we create an empty file favicon.ico that web browsers will ignore, and use the PNG instead.