Use case:

With the following code:

FooBar fooBar;
static final FooBar FOOBAR = ...;
:
fooBar.someMethod();
:

and desire to modify the name of the Class and the variable it should be 
possible to do this in a single Find and Replace  by using:

find text:    foobar
replace text: mooBlah

should result in a code:

MooBlah mooBlah ;
static final MooBlah MOOBLAH = ...;
:
mooBlah.someMethod();
:

Notice how the case of the original Class name, variable and static final 
variable and the uppercase B in replacement text were used as hints to achieve 
the functionality.

This is supported by emacs and is described like this in the emacs manuals:

REF: http://www.gnu.org/software/emacs/manual/html_node/Replacement-and-
Case.html#Replacement-and-Case

"
20.9.3 Replace Commands and Case
If the first argument of a replace command is all lower case, the command 
ignores case while searching for occurrences to replace—provided case-fold-
search is non-nil. If case-fold-search is set to nil, case is always 
significant in all searches. 

In addition, when the newstring argument is all or partly lower case, 
replacement commands try to preserve the case pattern of each occurrence. 
Thus, the command 

     M-x replace-string <RET> foo <RET> bar <RET>

replaces a lower case ‘foo’ with a lower case ‘bar’, an all-caps ‘FOO’ 
with ‘BAR’, and a capitalized ‘Foo’ with ‘Bar’. (These three alternatives—
lower case, all caps, and capitalized, are the only ones that replace-string 
can distinguish.) 

If upper-case letters are used in the replacement string, they remain upper 
case every time that text is inserted. If upper-case letters are used in the 
first argument, the second argument is always substituted exactly as given, 
with no case conversion. Likewise, if either case-replace or case-fold-search 
is set to nil, replacement is done without case conversion. 
"