If you are dressed casually or even informally it really does not matter. I am kilted all day every day and sometimes go almost all week without wearing a sporran at all, particularly when I am wearing a jacket with sufficient pockets to hold my wallet, coin purse and handkerchief. Unless I am dressed formally, my keys always hang from a key-clip on my belt. I guess I wear a sporran more in the summer since I am less likely to be wearing pockets above the waist (ie: in a jacket!).

On the other hand, when formally and semi-formally attired, I always wear a sporran, together with the sgian dubh and garter flashes - it is part of the 'kit'.

I would never wear a sporran to make my kilt look more like a kilt! To do so smacks of personal insecurity. The sporran is nothing more than a pocket, except when it is part of a uniform or, as I said, a more formal outfit. When dressed casually without all the other accessories, I see no need to treat the sporran any differently to those.