Actually the eval { ... }; if ($@) { ... } pattern is dangerous. Consider this example:

use 5.010;
use strict;
use warnings;

sub DESTROY { eval { "no error here" } }

eval {
    my $x = bless {};
    die "an error here";
};

say $@ ? "ERROR" : "no error caught";
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This reports no error caught, because $x goes out of scope, the DESTROY method is called, which in turn executes an eval that rests $@. Hooray for global variables. (This is one of the reasons that Perl 6 has context variables instead).

A safer meme is

my $success = eval { ...; 1 }
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So back to the question, what's the difference? It's that in the case with eval and if the code doesn't work as expected if some DESTROY method forgot to localize $@.