I think the question of when references to subs are used and anonymous subs are used is too broad.

Here is a simple example of anonymous sub -

my @sorted = sort { $a <=> $b } @unsorted;
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In the above block we passed an anonymous sub to sort. It is just easy (convenient) to write numeric sort that way than to define a sub that returns  $a <=> $b

An example of sub ref is signal handling

$SIG{INT} = \&catch_int;
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These examples are very simple. Others might contribute better examplese. Another thing i can think of is closures where you return a reference to a sub from inside another sub.

-SK