Your own visits are left out of the numbers

On a small site the people who look at it most are the people who built it. A designer refreshing a page forty times in an afternoon can be a tenth of the month's traffic, and every number after that — time on page, bounce rate, which page is most popular — is describing your own team rather than your customers.

It matters most on exactly the sites where the traffic is small enough for the decisions to be hard.

In GA4 it is Admin → Data Streams → Configure tag settings → Define internal traffic, where you add your office IP range, and then Data Settings → Data Filters to switch the "Internal Traffic" filter from Testing to Active — it does nothing until you do.

In Plausible and Fathom it is a browser setting or a localStorage flag rather than an IP, which works better for people who work from home.

Tick this when the filter is active, not merely created.