I used Kingo to root S2 and S4 without any issues. I also used it on HTC and another phone, when no other known way to root was possible. Only device I had issues with was HTC Diamond (old) and mini HTC model - probably MY Fault!!! So Kingo does have benefits! I forget the model of device that, but nothing would work.
#0. Connect phone to PC and execute a full phone backup using ADB.
#1. Backup all SIM + Google Account contacts.
#2. Remove SIM card and optionally insert old/dead SIM.
#3. Remove ALL Google accounts. All email accounts, calendars and contacts should be removed. Delete if still there. All data will be later re-added and populated with next re-sync after addubg accounts. I don't trust Root toolkit not to steal this data...
#4. Remove non-root applications - e.g. BK Package Disabler (export XML). Later update to newer root-friendly Disabler. Import XML to auto-disable everything.
#5. Use a FIREWALL on PC and Android during root process. Accept and reject each requests for network access - You will use a USB cable and run the EXE installer on your computer. Repeat trial-and-error until root procedure finishes for your privacy, or skip if you do not have any concerns (e.g. new device or all personal data already removed).
What else... What have I forgotten? SMS backup I guess...
After root, repeat with another full ADB backup. Keep ALL your backups and always give them sensible file names - 2017.07.24-S5-Stock-NoRoot etc.
Someone needs to write an updated list of concise steps to replace the Kingo SU with SuperSU, so that you do not lose Root in the process, or cause any issues. (I used Titanium to freeze Kingo SU and install Super SU, however had ongoing messages about binaries...

I suspect file names were conflicting.
But you can always copy SuperSU to SD card and the reboot into recovery or boot, and install it that way, to get KingoSU out of the way. Exact steps with pre/post would be helpful for everyone though.
But the 2014 KingoSU was fine. Had no issues with it. It had diagnostics and logging. For most people, they just want root, plus prompt to allow/deny access.
I just HATE those apps that check for root and then reject/deny operation... Why they have to stop workign if they detect root access. 3 apps I use do this, and I have not rooted my current phone...

---------- Post added at 02:15 PM ---------- Previous post was at 02:13 PM ----------
BTW 'KingRoot' and 'King
oRoot' are DIFFERENT!
Do
NOT use KingRoot!!!