Because

say $instance;
[download]

say $instance->as_string;
[download]

That's it. Because it's nice.

And it's not like it takes anything away. When's the last time you saw Class=HASH(0xDEADBEEF) and thought it was useful?^[1]

But it's best to give the choice, though.

use overload '""' => \&as_string;

sub as_string {
   my $self = shift;
   ...
}
[download]

1. The overload module provides a function to get that stringification if you really do need it. Also, the referenced var type, its address and the class associated with it are all available through Scalar::Util functions.