"Variables are usually constant"?

[James R. Meehan <Meehan at YALE>]

"A variable is a named place to put something.  Variables are named
by identifiers.  This use of the term variable may often be confusing
since the values of most variables never vary -- variables are usually
constant."  (T Manual, page 5)

Could you elaborate?  Do you mean that once a variable is assigned
a value, it doesn't usually get a different one?  This is a debatable
point, but I think it's not worth going into in the manual.  It's too
confusing.  Any objections to removing it? (Another example of "flesh out
or flush")
-------