Tampering with your console is against Sony's terms of service, so if your console dies and their repairmen find out that you hacked it, they can refuse repair even if it didn't die due to your fault because that's how the world works sadly. I don't think you can brick the console during the jailbreak process unless you try really hard, but you can definitely brick it if you don't know what you're doing after the exploit. It is unknown if the ps4 stores logs in its flash memory (not on the HDD). Unless you restrict your internet connection, it is possible for the ps4 to communicate with Sony's servers and even if you don't get banned, they can store information that your console has been hacked to prevent repair, who knows. Developers include the warranty clause so then people cannot be upset at them that they bricked their own console and Sony refused repair. Also, the permission escalation exploit itself might not be permanent, but the things you do with the exploit very well can be permanent.
What should you do to avoid those risks? Don't install software from unknown sources and if you don't know what an option / button does (for example in debug menu) then do not use it / mess with it.
And it's always wise to make a backup before jailbreaking, at least of your save files in case things go wrong.
In case of 9.00, don't forget to unplug the USB drive as soon as the exploit succeeded.
