If a kitchen is a collection of work centres, and how each work centre relates to each other is important to the "flow" of the kitchen, then it's important not to put obstacles in the middle of that flow. NKBA Guideline #4 states that a full-height, full-depth, tall obstacle (such as a tall pantry, refrigerator or wall oven cabinet) should not separate two primary work centers.
The top illustration on the left shows a wall oven cabinet to the right of the cooktop. This may be viewed as a convenient placement (keeping all the cooking centres together), but by interrupting the countertop we've interrupted the work flow.
Guideline #5 seems a bit obvious at first glance, but you'd be surprised how many kitchens quite literally trample all over it. No major traffic patterns should cross through the basic work triangle. Think of it this way: if the primary path to the back patio runs directly across the path between the sink and the fridge, how many times will you be interrupted by stampeding kids while preparing for a BBQ?
The illustrations shows one of the simplest ways to avoid this mistake. An island can clearly define the footprint of the kitchen, and will nicely direct non-kitchen traffic away from the work spaces.