At the present time, best rules and patterns have reached a zenith in popularity and diffusion, thanks to the software communitys efforts to discover, classify and spread knowledge concerning all types of rules and patterns. Rules and patterns are useful elements, but many features remain to be studied if we wish to apply them in a rational manner.The improvement in quality that rules and patterns can inject into design is a key issue to be analyzed, so a complete body of empirical knowledge dealing with this is therefore necessary. This paper tackles the question of whether design rules and patterns can help to improve the extent to which designs are easy to understand and modify. An empirical study, composed of one experiment and a replica, was conducted with the aim of validating our conjecture. The results suggest that the use of rules and patterns affect the understandability and modifiability of the design, as the diagrams with rules and patterns are more difficult to understand than non-rule/pattern versions and more effort is required to carry out modifications to designs with rules and patterns.