What is in the page
- One stylesheet,
button.css, loaded in the head so the button does not flash into place at the bottom. It is the plugin’s only file for visitors. - A few lines of markup in the footer: a link, or a
<details>menu with up to eight links. - Icons drawn inline as small vector paths, so there is no icon font and no image to fetch.
- A short inline style with your colour, size, distance and layer, so changing them does not mean another file.
What is not
No JavaScript, unless you turn on the Analytics option, which adds one short inline snippet. No web font, because the text uses the font your theme already loads. No call to WhatsApp, Telegram or anyone else while the page loads: the links are only followed when someone taps them.
On the server
The settings live in a single option that WordPress loads together with its other options, so showing the button adds no database query of its own, and a visit never writes anything. The admin screens are loaded only in the admin. If something goes wrong in drawing the button, the page is served without it, rather than with an error.
The only part you can slow down
The button is as fast as the page it is on. If a speed test blames your site, look at the scripts first. A button that needs none is one thing less to wait for, and it keeps working when the page is cached.