abap/activate_precompiled_header is a SAP Parameter attribute which is used to control Mode of Operation of Precompiled Header Usage information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
With the aim of improving its performance, the ABAP Compiler can use
precompiled headers, which store the declaration data of global classes,
global interface, type groups, and TOP includes in a cache for quicker
access.
This profile controls the operation mode in which the precompiled
headers and generated and used by the ABAP Compiler.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.