The major strength of the federal budget process is that it is very democratic. Many people, both inside and outside of government, have the chance to influence various aspects of the budget. It must be passed by both houses of Congress and signed by the president. This is a great deal of democracy.
The major weakness of the process is that it gives too many people the ability to add “pork” to the budget. It is easier to add things to the budget (thereby making one group or another happy) than to take them out (making some group very angry and not really pleasing anyone very much).