One of the key functions of a person's ego network is to help cope with the problems of daily life. Friends & family give you rides when your car is in the shop. They help you move into a new apartment. They walk you home from bars at 2 am. It has been shown in a large longitudinal study (Berkman and Syme, 1979) that people "who lacked social and community ties were more likely to die in the follow-up period than those with extensive contacts."
It appears that there are at least four basic categories of support that one gets from others:
In industrialized societies, social support tends to flow through equals -- peers. That is, our friends figure prominently in our support networks. In contrast, in agricultural societies, aid tends to flow through hierarchical relations like parent-child and boss-worker.
According to Social Resource Theory (Lin 1982), strength of tie is related to the kinds of resources provided. Instrumental actions (buying goods, looking for a job, looking for a mate) require diverse social resources and therefore tend to be accomplished via weak ties (one reason is that we tend to have strong ties with people who are similar to ourselves, so diversity is achieved through weak ties). Expressive actions (sharing life experiences, emotional support) are more likely to be done by strong ties.
Kinship ties tend to be used for really big things, like life-threatening emergencies. One reason for this is the cultural understanding of the obligations of kin -- they are supposed to help. Another reason is that the dense ties among kin make it easy for them to mobilize and coordinate their efforts. A person's friends may not even know each other, but kin typically do.
A large chunk (25%) of active ties in a support network are local. This means that even in today's world of high mobility and excellent transportation and communication media, we still get a lot of our support from people who are physically close by. It is not a virtual world yet!
Social support is not clearly related to similarity of ego to alter. That is, one gets social support from both people who are similar to one's self, and different from oneself. However, with respect to age, there tends to be a lot of social support provided by people of dissimilar ages. Young people tend to provide older people with physical labor, while old people tend to provide knowledge and impart skill to younger people. Also, with respect to employment similarity, people with similar employment status tend to give aid to each other.
Size. In general, the larger a person's ego network, the more support they receive. This is basically because there are more people available to provide any service you may need. In addition, it appears that alters in larger networks tend to provide more support. It is unclear why this should be so, but it may be that the alter perceives the ego as important (because they are so well connected) and therefore deserving of more help.
Density. The density of an ego network is defined as the number of ties in the network divided by the number of pairs of people. If T is the number of ties (not counting ties to ego), and N is the number of people in the ego network (not counting ego), then the formula is:
2T
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N(N-1)
The relationship of density to social support is not yet clear. It is thought on theoretical grounds that density promotes mental health, but that has not been shown yet empirically. What is clear is that dense ego networks tend to better at providing emergency and chronic health care.