[Samsung Galaxy S20 FE Guides, News, & Discussion] Leoev:
My experience rooting S20+ Exynos 990 following this thread:

TL;DR: Added 6-8 hours of standby battery life just from turning off prime and big cores, haven't checked on screen battery life since I don't use my phone much at work, but I wanted standby time improved.

Before turning off the prime and big cores, I got 11 hours tops on battery life. Seemingly out of nowhere the phone was always warm, despite just sitting at my desk with a very strong signal. I knew that at 12 pm, with 50% brightness, 120hz, and AOD I would expect at least 50% just gone even though I barely even used the damn thing. The straw that broke me, is that even though I was connected to wifi, I could only expect maybe at most, 3-4 hours of screen on time, which finally drove me insane. I checked out the thread sometime ago but was skeptical if it really was worth the trouble since it seemed a lengthy process. Take it from someone who hasn't rooted in a long time, just follow the guides and it all is pretty simple.

After turning off the prime and big cores, immediately thermals were so much better, after 3-5 minutes the phone was much cooler, about 5-8 degrees cooler on the chip area. Since the phone was reset, I couldn't really tell if battery was better. After the using my phone for a week rooted I can tell you, the battery difference is abysmal.

Before, I was struggling to end my day on 30-20%, now I can confidently end my day on 60-50%, depending on how much I used my phone. When idle the phone, barely sips battery, my estimate is that it went from 8-10% just idling, to 3-4% (need to check since I haven't turned on the prime cores ever since rooting). I wasn't willing to sacrifice 120hz so I always kept it on and battery life was good, however I will test with Max Hz on 96 hz, which should extend battery life.

Performance on the little cores is virtually the same, I haven't noticed any hiccups, lag or anything by that matter. I was concerned that on this thread it was mentioned that the camera took a hit, but on the S20+ nothing has changed, maybe the shutter is 0.3 seconds slower but I honestly don't notice or it doesn't bother me at all. Recording high resolution videos is no problem, and nothing really changed for me. Thermals are massively improved, if you're doing a heavy task, like recording, downloading or uploading, or something that you know requires heavy lifting, of course the phone will get warm, but not even close to how hot it would get just idling or doing the same tasks with the big or prime cores.

Since I don't play games I can't really say whether gaming has taking a hit or not, I would say that it depends on the game you're playing. You can always create a profile that enables the prime and big cores on FKM.

Overall I can say this, if you have an exynos 990 phone and getting real sucky battery life, rooting is the way to go. This phone just feels so much better with this extended battery life, and now rooting allows me to mod it as I want it or turn off things that weren't useful. Just be warned you will lose Google Pay and some apps from Samsung that use Knox, but for me what you get in return is so much valuable.

Please let me know if you have other questions from rooting the chip.