From a strategical standpoint, it would have been better if Japan invaded Russia from the East so Stalin couldn't move his Siberian reserve units to the West; making Germany's invasion easier. If Hitler didn't order the his troops to stop before Moscow, Germany very well could've taken it and the tide of the war would've been changed. This could've been the few times in history where Russia could've successfully been conquered having two major powers attacking it on both fronts. Japan's attack on Pearl Harbor forced Germany to declare war on the US which eventually would lead them both to be defeated.
Japan needed oil to modernize and supply its military; the globe (and particularly the US) had stopped selling its oil to Japan because of Japan's invasion of Indochina; the only way left to grab oil was to take it forcibly from US allies like the Philippines and Holland's East Indies, and the US was the only naval threat in the region; the idea therefore was to knock out the US's will to resist (and some of its capacity to respond) quickly and nab all the oil sources at once.
The 1941 De Facto Embargo on Oil to Japan: A Bureaucratic Reflex. Irvine H. Anderson, Jr. Pacific Historical Review Vol. 44, No. 2 (May, 1975), pp. 201-231.
To add some additional depth to /u/overzealous_dentist's answer, /u/kieslowskifan wrote a masterful answer to a similar question recently: https://www.reddit.com/r/AskHistorians/comments/3ugros/why_did_japan_not_assist_in_germanys_invasion_of/cxes5a2