It's a critical part of active directory.
Description The Netlogon subkey stores information for the Net Logon
The Net Logon service verifies logon requests, and it registers,
authenticates, and locates domain controllers. Also, to maintain
backward compatibility, Net Logon manages replication of the user
account database to back up domain controllers running Windows NT 4.0
Restoring depends on how it became missing.
The netlogon share is different. It's a share on domain controlers for logon sripts.
The administrative share for the scripts folder on Microsoft Windows
NT domain controllers at %SystemRoot%\system32\repl\import\scripts.
This share is used by the NetLogon service for the following purposes:
Storing a default user profile for users (which must be stored in a
subdirectory called Default User). If a user without a local profile
on his or her workstation or a server-based roaming profile logs on,
the default user profile is used. Storing logon scripts (for example,
logon.bat). Storing system policies (ntconfig.pol or config.pol
files). When a client logs on to a Windows NT domain and is
authenticated, the final step in the logon process involves connecting
to the NetLogon share and downloading or applying any of the items in
the preceding list.