Traditionally plusargs switch is used in verification environments to configure attributes of the verification environment from the command line, like configuring timeout value of the test environment, configuring no of packets to be generated by the generator and setting error limits for the test to exit simulation. More compact and robust implementation of configuration mechanism in VMM is through vmm_opts. vmm_opts class has methods like get_object_bit(), get_object_int() to receive the runtime values in the environment. We can set different values to different instances from the command line. Example you can use the same configuration attribute for configuring no of packets for both TX as well as RX transactions and hierarchically set different values for TX and RX from the command line. Configuring global values like the test bench timeout does not require hierarchical access. The values can also be overridden from the test case using set_int () and set_bit() methods in place of a command line override.
Configurability of test bench from command line is a must have feature especially to abstract your test bench complexity from the consumers in this case a RTL designer , test case development team or release management team.