Web 2.0 sites have lots of tiny javascript/css files, which causes one extra round trip per file to the server and back! This is bad! Bundle-fu throws it all up into a big package and sends it out all at once.
Rails Long Term Support
Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)
Prevents you from data breaches and liability risks