The idea of using a proxy is about protecting information. If you don't care about the fact that people know which websites you access than a proxy might not help you.
To give you an example, a while ago I wanted to find out who wrote a certain edit to a Wikipedia page. That edit wasn't made with a nickname so the IP address was public. By having access to the IP address I could see that the edit was made person who lives in the city in which a person I suspected to have written the edit lives.
I know a hacker who had a conversation with a journalist. When the journalist told the hacker that she visit his website he knew the time the journalist visited because the browser send enough information to the webserver to identify the company behind the web request.
If you are a huge company and some journalists wants to write a piece about your company than you have a huge interest in knowing which parts of your company the journalist cares about.
The journalist on the other hand wants to catch you off guard. If he thinks you are hiding some scandal he doesn't want you to have any information about the research process that the journalist used before the interview.
Let's say you are a business A and want to buy item X from company B. There are 5 vendors who all sell item X but company B is the only one that offer feature P. For most business feature P isn't very important. For business B it's very important so the representative of business A spend a lot of time looking at the way feature P is described on the corporate web site of company B.
If company B knows, that information can inform their negotiating position. They can ask for a higher price because they know that company A want Y and they are the only company with feature Y.
Companies care about what information other companies have about them and usage of proxies is a way to reduce information leakage.
On a more personal level, you might share a WLan with a neighbor and not want that neighbor to know that you look at porn websites. A proxy can help you.
If you get banned from a forum and try to register a proxy will make it harder to catch you in your attempt.
Those examples I gave don't require any access to the ISPs. If you are living in China but don't want that the Chinese government knows which websites you browse then a proxy provides you a useful tool. It allows you to circumvent the Chinese firewall and access all websites.
Even in Western countries there are websites that get censored and which you might access freely by accessing them from another country. Chilling Effects provides many examples. Noteworthy is that certain far-right political content can't be found on Google if you use a German IP address.
There were times when Australia censored parts of the political Wikileaks website.
Apart from censorship of political speech there also straight commerical censorship. While China didn't censored the video "Ai Weiwei does Gangnam Style" because of political reasons the GEMA pushed Youtube in Germany to censor it because Google doesn't have an agreement with the about the right to Gangnam Style.
For similar reasons a lot of Youtube content isn't usable with a German IP.