Explanation

For the SharePoint Server

Explanation

SP_Services is a domain account used for the Service Applications Pools.  ex: When you create a Managed Metadata Service application and create a pool for it, you select this account!

SP_Crawl is used within the Search Service Application  to crawl content. The Search Service Application will automatically grant this account read access on all Web Applications. It will also run the SharePoint Windows Search Service.

SP_UserProfiles is the account used for the User Profile Synchronization between your Service Application and your Active Directory. This account does not need any local rights, however you need to give it Replicate Directory Changes rights on the Active Directory in order to allow the synchronization

Medium Security Option (Sweet Spot)

SUMMARY

For the SQL Server

Explanation

For the SharePoint Server

Explanation

In the Medium Security option we increase the security by adding two new accounts: The SP_Admin and the SP_Search. Instead of giving all the Farm Administration power to the SP_Farm account, the SP_Admin will be the one that installs and configures SharePoint 2013 and have the local administrator rights, while the SP_Farm will only run the services and connect to the database. Furthermore, instead of letting the SP_Crawl account run both the Windows Service and have FULL-READ rights on all the web applications, the SP_Search will now run the Windows Service. Here is the breakdown of the accounts:

SP_Farm is a domain account that the SharePoint Timer service and the web application for Central Administration use to access the SharePoint content database. This account does not need to be a local administrator. The SharePoint configuration wizard grants the proper minimal privilege in the back-end SQL Server database.The minimum SQL Server privilege configuration is membership in the roles securityadmin and dbcreator.

SP_admin is a domain account you use to install and configure the farm. It is the account used to run the SharePoint Configuration Wizard  for SharePoint 2013.The SPAdmin account is the only account that requires local Administrator rights. To configure the SPAdmin account in a minimum privilege scenario, it should be a member of the roles securityadmin and dbcreator on the SQL server.

SP_Services is a domain account used for the Service Applications Pools.  ex: When you create a Managed Metadata Service application and create a pool for it, you select this account!

SP_Crawl is used within the Search Service Application  to crawl content. The Search Service Application will automatically grant this account read access on all Web Applications.

SP_Search Is used to run the SharePoint Windows Search Service.

SP_UserProfiles is the account used for the User Profile Synchronization between your Service Application and your Active Directory. This account does not need any local rights, however you need to give it Replicate Directory Changes rights on the Active Directory in order to allow the synchronization.

High Security Option

SUMMARY

For the SQL Server

Explanation

The difference between the Medium Security and High Security Option is that we now have a separate account for each of the two base services: SQL_Agent and Database Engine.  Nothing changes for the SQL_Admin

For the SharePoint Server

Explanation

The only difference between the Medium security and the High Security option is that we now have a separate account for the Web Application Pool hosting the ‘My Sites’  since it has a different security policy than the other Web Applications .  I will only give the details for the new account in the breakdown:

SP_MySitePool  is a domain account used for the My Sites Web Application Pool Identity. It’s very similar to the SP_Pool, however it is only used for the My Sites Web Application.

Source: http://www.absolute-sharepoint.com/2013/01/sharepoint-2013-service-accounts-best.html
You can download all the information here in PDF format on  here: http://sdrv.ms/U6hvuU