It depends on whether the system you're using overcommits memory. Some OSes (eg Linux) provide settings to limit virtual memory use to some percentage of physical memory. See http://engineering.pivotal.io/post/virtual_memory_settings_i...

The only time you should avoid checking malloc() return values are for special mallocs that really cannot return NULL. One example is FreeBSD's kernel malloc() when called with the M_WAITOK flag.