I sometimes get lax and don't count everything- a bite of my BF's dinner, a tsp of sugar in my coffee. But I should. And the minute my weight starts stalling is my signal to tighten the belt and really get nitpicky on counting calories. I always know that's the first thing I'm "fudging" and the first behavior I need to correct before I start whining about a plateau.
Yes, tsp of oil, butter, vinaigrette here and there are the most important small thing to count- they are some of the most calorie-dense food we eat. Not counting a tbsp of oil is like choosing not to count Fiber One bar or a can of tuna- definitely something substantial you want to include in your count
Re. fruits/veggies- I have also heard that some fruits/vegetables are "negative" but in my opinion either you calculate ALL the calories burned from your BMR that day and subtract it from your calories to get your deficit, or you calculate none of it. I think when we start picking and choosing which foods our bodies already burned off ("I won't include this carrot because my body is burning it off as it's digesting it") we start going down a potentially slipper slope which I've definitely done ("I can drink this Starbucks latte as my rewards for working out- it's only 120 calories so I already burned that by exercising").
Basically I think the more we omit the less accurate our calorie count is and the looser a handle we have on how much we are actually intaking