This is because of Qualcomm MP-Decision that controls the hotplugging, that tells the CPU to boost MIN freq to 1190 Mhz to fake UI smoothness and response, about 2-3 second then ramp quickly down to 300 Mhz, and then do the same over and over again. Good for performance, bad for battery.
This is also a part of Qualcomms own Project Butter solution - using / forcing the device into overdrive mode w/o any thoughts on heat generation / stuttering by nearly
instant & uneven shifting between frequencies, thanks to a built-in touch boost
feature that is boosting the phone to 1190 Mhz in Z1 case, was at 1026 Mhz frequency spectrum at Z / devices that used the same QC shipset as the Z.
This is fixed by @faux123
in his rewritten Intelliplug module, that conserves / keeps the performance (even improves it..) and boosting battery life with a more natural step pattern through your device various CPU clock frequencies.
EDIT: More easy understood info on those two links!
Sent from my Xperia Z1 using XDA Premium 4 mobile app
Android Devices that I am using:
1. Sony Xperia Z1 - ROM: iHackers v5.0 Beta / Kernel: TrinityUltimateKernelV2.4AC_0 - Stable Release
2. Sony Xperia Tablet Z - ROM: Stock 10.5.A.0.230 / Kernel: Stock kernel