What are the impacts of information prevalence on a service system? We study a single-server queueing system where customers arrive according to a Poisson process and service takes an exponential time. There are two streams of customers, one informed about real-time delay and one uninformed. We characterise the equilibrium behaviour of customers who may balk in such a system and investigate how a marginal increase in information possession (i.e., a larger fraction of informed customers) would affect the system in terms of performance measures such as throughput, service accessibility, individual welfare, and social welfare. We show that the impacts of information prevalence on system performance measures are determined by the equilibrium joining behaviour of uninformed customers. Perhaps surprisingly, we find that throughput and social welfare can be unimodal in the fraction of informed customers. In other words, some amount of information ignorance in the population can lead to strictly more effcient outcomes, in terms of the system throughput or social welfare, than information homogeneity. For example, for a critically loaded system (i.e., the implied utilization is 1) in which informed customers have a joining threshold no less than 2, throughput would always suffer if there are more than 58% of informed customers in the population. When a general system has an implied utilization suciently higher than 1, there is always a critical level in (0,1) on the fraction of informed customers beyond which social welfare suffers.