Just curious if this is really useful, because it can lead to infinite loops that are hard to figure out.
if by useful you mean used with this particular behaviour in mind (turning a continue
block into a loop, not necessarily an infinite one), yeah probably. If not in clean code, maybe it is used as an obfuscation. Maybe without that precision in the doc, someone would have still expected next
to mean "execute the continue block straightaway", even if this does not seem the more probable interpretation.
You could still obtain the behaviour you were expecting though, with:
next if ($try % 10);
print "Still running after $try tries\n";
will skip execution of the inner block. But it does not help readability.