One thing that advertisement does for us is to keep us in touch with what is popular and what people are talking about. A lot of ads have worked their way into popular culture over the years, and if you do not watch the ads, you don't know what everyone is talking about.

I don't have television (by choice), and I find that sometimes I have to go to YouTube to watch an advertisement to "get" a joke or a comment that I hear.

Advertisements work because they sell something. When people see and/or hear an advertisement, they are (presumably) being given information which could (presumably) impact their lives. Ads tell us about things to do and available products as well as try to move us to act, as is the case with political ads, for example. Many ads establish and promote a brand even more than any specific product, and these ads are often responsible for memorable characters (such as the Geico gecko, the Aflac duck, or Flo the Progressive Insurance lady). Whatever their purpose, if advertisements are not effective, they are short-lived. 

A lot of ads should show us that we need to be very careful about the negative side of the society we live in. As a capitalist society, when it comes to business, people are basically in it for themselves and have very little incentive to be truthful just for the sake of being good. When we look at ads critically, we see that this is how our system works, for better or for worse. The more knowledgeable we are about that, the better off we'll be.

Also, don't discount the humor factor. Many ads give us something to laugh at, which is not always the advertiser's intention.

If we are critical in the way we read/watch/listen to ads, they can help us understand the choices we have. They also, as others have mentioned, enable us to comparison shop without leaving the house. They can also stimulate competition. If I own a hardware store and I see on TV that the owner of the hardware store across town is underselling me, it will force me to make some choices that can be beneficial to the consumer.

I think one of the ways advertisements help our daily life is by simply making us aware of opportunities we might not otherwise know about.  Perhaps there is an event you would be interested in but didn't know it was going to be in town.  Maybe there is a sale or a special at your favorite store or restaurant.  Advertising helps people meet their needs and desires by giving them knowledge of events important to that person.

Advertising can help us in at least two main ways.  

Ads can help us to understand our society better.  They show us what sorts of ambitions people have because they show us what our society thinks people's lives should be like.

On a more practical level, some advertisements help us economically.  These ads can help us to save money.  They do this by telling us what goods are on sale in which stores.  By looking for ads like these, we can save ourselves money by buying things when they are on sale instead of buying them for full price.