Four tags from one button
HubSpot's own FAQ answers why a landing page URL gets so long after a CTA click. HubSpot appends four parameters, __hssc, __hstc, __hsfp and hsCtaTracking, which it says are "necessary to register views, submissions, and clicks for your CTA." It then splits them by job: "The __hssc, __hstc, and __hsfp parameters are used for cookie tracking while the hsCtaTracking parameter is specific to CTA tracking." Of the four, hsCtaTracking is the only one about the button itself.
A legacy tool
These parameters belong to HubSpot's CTA (legacy) tool, and HubSpot says accounts created after March 17th, 2025, do not have access to it. The click goes through HubSpot first: the button sends the visitor to a click tracking URL, which records the click against the CTA, then redirects to the final page. That extra hop is also why a legacy CTA pointing at an anchor on the same page reloads the page before it scrolls.
The cookie tags beside it
HubSpot's cookie documentation describes two of the neighbors. __hstc is its main cookie for tracking visitors: it holds the domain, your hubspotutk visitor ID, timestamps for the first, last and current visit, and a session number, and it expires in six months. __hssc keeps track of sessions, including a count of page views, and expires in 30 minutes. Those two describe the visitor's own browsing, while hsCtaTracking describes the CTA they clicked.
If you share the link
The page itself does not rely on hsCtaTracking. HubSpot uses it to count views, submissions and clicks for the CTA, so removing it costs the site owner that click in their CTA reporting. The cookie values are the part worth thinking about before pasting a copied link somewhere public, since HubSpot's __hstc carries hubspotutk, the ID HubSpot uses to recognise you as a contact, along with your visit timestamps and session count. HubSpot's email links use _hsenc instead, and its ad links use hsa_cam.