There are many specific reasons to get support from government, and some can be considered better than others (and these reasons may ordered accordingly). This list includes the main reasons to get government support generally:
1) unfortunate circumstance like illness, injury, weakness, disability, natural disasters, bad luck, etc.
2) too difficult to support yourself because the way society is (in terms of what society values (or does not value)), is too divergent from your way (see my rehabilitating to a sustainable way of life document for an example)
3) epidemiological needs such as civilian infrastructure (and in overly fear-based / "real"? (fear-based) world, military might/leverage/action)
4) a belief that basically justifies that the government took from you, therefore you have a right to take from the government
5) opportunistic in a bad way, like a cheater or stealer, and can exploit the system