Just use a proper data structure and you don't have to worry about splitting or temporary arrays.

my %cmd = (
            Mon => [ qw( Jim ) ],
            Tue => [ qw( Jim Paul ) ],
            Wed => [ qw( Jim Paul Annie ) ],
          );

print scalar @{ $cmd{ $_ } }, " can't make it on $_\n"
  foreach keys %cmd;
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perldoc perldsc, perldoc perllol, perldoc perlreftut

But to answer the original question, no it's not necessary. split in scalar context does the right thing.