Normally if you do ./foo.sh your script is run in a subshell so whatever happens in that one is not affected by the caller shell.

I wanted to write a script to affect the caller, eg shortcut cd-ing for example.

touch foo.sh

echo "cd /tmp/foo/bar/baz/$1" > foo.sh

./foo.sh "yolo" # No effect at all

. foo.sh "yolo" # Your current dir changes to /tmp/foo/bar/baz/yolo

You can also put this into ~/.bashrc as an alias so you can easily call without remembering the full path

alias void='. /a/b/c/foo.sh'

source ~/.bashrc 
void  # Thank me later.