If you put that expression at the end of another expression then, even if the first expression fails the whole expression will still succeed, the exit code will be set to 0, and the code will keep running.

See set -e to stop script on failure and set -x to print statements as they are executed

examples/good.sh

#!/bin/bash
set -xe
ls examples/good.sh
echo $?

$ ./examples/good.sh
+ ls examples/good.sh
examples/good.sh
+ echo 0
0

examples/bad.sh

#!/bin/bash
set -xe
ls examples/no_such_file.txt
echo $?

$ ./examples/bad.sh
+ ls examples/no_such_file.txt
ls: cannot access 'examples/no_such_file.txt': No such file or directory
+ echo 2
2

examples/bad_without_e.sh

#!/bin/bash
set -x
ls examples/no_such_file.txt
echo $?

$ ./examples/bad_without_e.sh
+ ls examples/no_such_file.txt
ls: cannot access 'examples/no_such_file.txt': No such file or directory
+ echo 2
2

examples/bad_saved.sh

#!/bin/bash
set -xe
ls examples/no_such_file.txt  ||:
echo $?

$ ./examples/bad_saved.sh
+ ls examples/no_such_file.txt
ls: cannot access 'examples/no_such_file.txt': No such file or directory
+ :
+ echo 0
0

Explanation

There are two separate pieces of syntax here: