SAP Host Agent 
SAP Host Agent is installed automatically during the installation of new SAP instances based on SAP NetWeaver 7.0 Enhancement Package 2 or higher. SAP Host Agent is upgraded automatically as part of the SAP instance, when you patch or upgrade the SAP kernel. However, you can also install and upgrade SAP Host Agent independently from an SAP instance.
You only need to install SAP Host Agent separately in the following cases:
There is no SAP system or instance on the host.
The SAP system running on the host is based on a release lower than SAP NetWeaver 7.0 including Enhancement Package 2 or SAP NetWeaver 7.2 and the host does not yet have an SAP Host Agent.
You have upgraded your SAP system to a release higher than SAP NetWeaver 7.0 including Enhancement Package 2 or SAP NetWeaver 7.2 and the upgraded system does not yet have an SAP Host Agent.
SAP Host Agent provides you with the following features:
SAP instance discovery and inventory
SAP instance control
Database monitoring and management
System or instance provisioning:
Hosting the infrastructure of SAP NetWeaver Landscape Virtualization Management (LVM), formerly known as SAP NetWeaver Adaptive Computing Controller (ACC)
Hosting software lifecycle (SL) tools interfaces
Operating system monitoring:
Using saposcol
Using Common Information Model (CIM) based infrastructures
IBM i-specific features:
Dynamically adopted authorization for SAP kernel 7.20 and higher
SAP ILE daemon (SAPILED)
SAP Database Performance Collector for IBM i