use Module LIST is equivalent to:

BEGIN { require Module; import Module LIST; }
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So one _big_ difference is that use is executed at _compile_ time, whereas require is only executed at "run" time.

Generally I would always use use even if you don't export any symbols.

One place where require would be preferred over use is when you want to include a module only when it really is needed. So you'll see code like:

if ($type eq "Excel file") {
  require SpreadsheetReader::Excel;
  my $parser = SpreadsheetReader::Excel->new();
  ...
}
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