I don't understand -- you say "=" and ":=" are not the same thing, but give an example where they act the same? Practically speaking, using ":=" removes any do

I don't understand -- you say "=" and ":=" are not the same thing, but give an example where they act the same? Practically speaking, using ":=" removes any doubt when quickly skimming over old notes. It is nice to be able to easily separate what is defined and what is asserted in each of dozens of statements.