Whether you're buying or selling, having everyone logging in and creating profiles make it safer for everyone. Now you can see exactly who you're dealing with. Better yet, you can see if you have friends in common who can tell you whether the person you're dealing with can be trusted.
Besides safety what are the other perks of having a profile?
Profiles allow you to follow and be followed by other people eager to make deals on OLX. That way every time you post an ad, all your followers will be notified straight away that you've got something new to sell.