"Errors should never pass silently." is more relevant for `set -e`
Or consider the last example from the wiki link above:
set -e
f() { local var=$(somecommand that fails); }
f # will not exit $ ( set -e; foo() { f=$(false); }; foo ; ); echo $?
1
$ ( set -e; foo() { local f=$(false); }; foo ; ); echo $?
0
$ ( set -e; foo() { local f; f=$(false); }; foo ; ); echo $?
1