What is the objective of code benchmarking and what it does

Question

just from this url https://www.hanselman.com/blog/ExperimentsInOpenSourceExploringVcrsharpForHttpRecordAndPlayback.aspx

i came to know there is a library which people may use to code bench marking but i do not understand what is code bench marking and when to use it?

what kind of output and benefit i can expect from code bench marking ?

[Benchmark]
public async Task ReadFromCache()
{

    using (var httpClient = HttpClientFactory.WithCassette("example-test"))
    {
        var request = new HttpRequestMessage(HttpMethod.Get, "http://www.iana.org/domains/reserved");
        var response = await httpClient.SendAsync(request);
    }
}

 

Output:

        Method |     Mean |    Error |   StdDev |
-------------- |---------:|---------:|---------:|
 ReadFromCache | 684.1 us | 3.154 us | 2.796 us |

 

when i see the output just do not understand what it is showing........so anyone tell me what kind of output it is ?

where this output will be showing in console or debug window ?

please share the knowledge about code bench marking. thanks