When you hit ctrl+l for example in / directory you will be moved to addres bar and has ability too edit location lets assume that you want change it to /home/pcman/Desktop/
so you type /ho[tab]
now there is /home int your address bar but should be
/home/ so you don't have to type / by hand -- it is very inconvinient
then you type pc[tab] and again path is autocompleted without trailing /. Every shell/file manager i know append this character.