Allowing a student to take variety of courses outside his/her field of study is a topic that needs to be addressed especially at undergraduate level. I agree that universities should allow students for this.
Firstly, it develops understanding at broader level because the more you learn the more you grow. In addition, if there is diversity in learning, you may expect exponential growth in return. For example, in a nut shell a student of political science studies governance, political philosophies, public administration and world affairs. It is more likely that these students to join public administrative service that administrates different tasks generally includes construction, management and policy making. If these students get the general understanding of construction, tender and contracts, project management and the impact of environment through relevant courses, they can perform in a better manner as variety of subjects will aid them to understand the complexities of each and every domain.
Furthermore, it is so true that many student gets confuse during selection of fields. If they are allowed to study wide range of subjects, it will allow them to decide which path is better for them or where they can deliver their full potential. For instance, my friend started his business just after his bachelor in science. As expected he is struggling in management of his business. If he was allowed to study courses from the field of business, he might get expertise in this domain.
Finally, we are living in 21st century where the pace of advancement is much higher than our expectations. This demands to get excellence in multi dimension to be successful in this competitive era. If you are studying the field of quantity surveying, it may be overtaken by computers in coming decades; therefore get your excellence in multi dimension to uplift the probability of your employment and growth.
Let me conclude that to develop understanding at broader level, to unlock your full potential and the requirement of multi skills demand to allow every student to take a variety of subjects outside his/her field of study.