C ++ 11 initialization T {p, ...} vs T = {p, ...}

Question

In his new book , Effective Modern C ++, Scott Myers makes an expression in the section "Points 7: Distinguish between () and {} when creating objects", which:

I usually ignore the equals-sign-plus-braces syntax because C ++ usually treats it the same way as the curly-bracket version.

Considering the "usually" qualifier, how and when = { ... } differs from the usual { ... } ?