This Italian garden consistently using design elements of symmetry, order, an axial relation to the house, but what ties it together are the row of terra cotta pots. Though each one is slightly different, by keeping the same material and shape, the result is soothing. Villa Acton.
Being faithful to a single style is one of the most powerful aspects of a good garden. Consistency in design - where similar themes are repeated - results in a more soothing space. Some of the big decisions required by the garden designer are formal vs. informal, native vs. exotic, literal vs. metaphorical, man-made vs. natural,... Of course knowing when to shake it up can inject excitement into a design. It is the contrast of one exciting element amidst soothing repetition that makes it work.
Check out posts that show other examples of how gardens use rhythm and consistency.