It is potentially unsecure both as a process and with its consequences, but if you know what you are doing (carefully read tutorials and guides step by step especially if you have no beforehand experience) you have a very low chance to brick your device or corrupt it in any other way.

It’s important to note that rooting is different from device model to device model and especially from manufacturer to manufacturer. Some manufacturers totally prevent rooting. Officially you lose the warranty of your device if you root it.

Some of the other commenters have mentioned that some apps check for root and refuse to work if the device is rooted (or only because the bootloader is unlocked) which is true, however if you are rooted there is variety of tools to prevent these apps from recognizing a rooted device (or just unlocked bootloader) so I wouldn’t count this as that much of a problem. I am using banking apps and google pay on my rooted phone just fine.