When you make a Layout, you have all objects that layout will use sitting in the layout.
A common thing people do in On Start of Layout Event is to Destroy all those objects, then they create them as needed. This is important to have these objects in the layout as it tells the layouts which objects to load into memory - if they are not in the layout, and if you do a Create Object action, it could cause your game to lag or pause while that object is loading into memory.
The drawback of having the object already in the layout and using an OnCreated Event is that, the original object sitting in your layout actually gets created - therefore triggers the event before the game even starts.
Personally I only use OnCreated to do cosmetic things, or things only pertaining to the object I'm creating.
I would recommend what blackhornet suggests or make global boolean to shut off the first time you are in OnCreated so it won't do the action on the very first OnCreate.