A Service Connection Point (SCP) is a marker created in an Active Directory container every time a SharePoint Farm is deployed.
This marker does not exist by default, you have to set it in your Active Directory. In addition, it is set at domain level, therefore, if you have multiple domains in your environment you must configure the use of this marker in each domain.
The purpose of this marker is pretty useful, especially in those DataCenters in which multiple farms (development, test and production farms) may coexist. Viewing this container we can keep track and have an accurate inventory of all SharePoint installations.
There are two major ways to check this marker: using Active Directory Service Interfaces Editor (ADSI Edit) or querying it via Powershell.
Once the SCP container is created every single new installation of SharePoint in the current domain will be registered.
Important: After creating the SCP container only new installation will be registered automatically. If you want to register any previous SharePoint installation you will have to do it manually.
It is also important that you also grant the Write and Create All Child Objects permissions right after the container is built to the Authenticated Users group to capture any (authorized or unauthorized) SharePoint installation.