leaving oil on a frying pan for use later I live alone, so I cook for myself. And often times I cook steaks/burgers on a pan, and later in the same day would return to use the same pan/oil without washing/using new oil.

Is this safe, or should one wash and use a new pan before cooking every steak/burger patties? I've actually done this for more than a day once (cooked burgers in the morning, steaks later that afternoon, and then burgers for the next morning).
If you preheat the pan then you should be perfectly safe as the high heat should kill anything 'dangerous' before you add your meat for the second meal.

That said, I would point out that those oils left out are likely to begin to degrade immediately, causing your steak to take on some potentially undesirable FLAVORS.