AFAIK you need to heat the pan to let the oil oxidize and polymerize¹ so that it will form a chemically protective and non-sticking coating.
If you wash your cookware with soap you will have to do it every time. For that reason some people don't wash cast iron at all and wipe it with a clean cloth or paper towel after using. (Burned oil is apparently not very tasty to bacteria and fungi so your pan stays relatively clean and bug-free.)
From my personal experience, meat sticks to untreated cast iron like glue, but on a well-maintained thick iron pan it glides like on Teflon.
¹ I don't know if it makes any chemical sense because all references to polymerized fats I could google up were in relation to reoiling (seasoning).