The Navigation Acts affected the American colonies both economically and politically. Scholars disagree as to how significant the economic impacts were, but they do not disagree about the political impacts.
One of the texts that I teach from (Carnes, The American Nation Combined Edition, pp. 84-5) spends over a full page on the issue of the effects of the Navigation Acts (and other English mercantile measures) on the colonies. It offers a number of ways in which the Acts did or did not have a major impact on the colonies. On the one hand, the Acts did prevent the colonies from selling certain things to other countries or to those countries’ colonies in the Caribbean. For example, Carnes says that tobacco planters in the colonies were hurt because England could not consume their entire product and yet they could not trade directly with other countries. Some scholars also say that the colonies were harmed by restrictions on trading things like wheat and rice.
On the other hand, Carnes says, there is evidence that the impact was minimal. He says that most colonial products did not fall under the Navigation Acts and could be traded freely. He says that the Navigation Acts were so poorly administered and enforced that they did not have a great impact for the most part even on those products to which the Acts did apply. He says that shipbuilding was actually helped by the Navigation Acts because the Acts helped British shipping, much of which was bought from colonial shipbuilders. Thus, Carnes argues that there were some economic impacts but that they were not severe. Some other scholars do not necessarily agree.
What scholars all agree on is that the Navigation Acts had serious political effects in the colonies. Regardless of whether the colonies’ economies were severely hurt, the colonists felt that the Acts threatened them. Moreover, they thought that the Acts infringed on their rights as Englishmen. Therefore, they resented and resisted the Acts. This resistance helped to build the overall resistance that led to the Revolutionary War.