I wanted to know if explicitly installing JDK on a machine is any different from copying the JDK folder to it from a machine where that JDK was installed?
The explicit installation might do additional things like setup the Path & possible create an uninstall link.
Other than that - I really don't think there is any difference in the two approaches.
The installation also updates your registry. Now I don't know if it only needs to do that to be able to use C:\WINDOWS\system32\java.exe and C:\WINDOWS\system32\javaw.exe, which are actually nothing more than wrappers that call the same executable from one of the actually installed JREs, but I still wouldn't try the simple copying myself, to be honest.