Since MOSFETs have a gate capacitance you’d want to limit the inrush of current from the output of a microcontroller to prevent it from getting damaged prematurely. That’s what gate resistors are usually good for.
Another thing is that most MOSFETs don’t fully activate with a gate voltage below 10V (n type) so usually a microcontroller pin isn’t good enough for switching large loads.
I have a 24V system and have made a voltage divider using two 10k resistors to step down 24V to 12V as gate driving voltage which is pulled down with a weaker MOSFET. The power MOSFET essentially ends up with a 10k gate resistor this way meaning it will take a bit longer to fully saturate.
Is too high harmful? In this situation the load is a heater that activates when the room temperature drops below 18C and deactivates when it gets above 22C so fast switching is not an issue.
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For something that’s not switching at a high frequency, slow rise and fall times are fine as long as you are staying within the safe operating area of your MOSFET. A 10K gate resistor could certainly work, but it will depend on your MOSFET and load.
It really depends how much power/current you are switching. If you are switching 1A with a beefy heatsink FET, the time spent in the linear region is short enough it shouldn’t be a problem. If you are switching 50A though it then you might have a problem. Depending on how that gate divider is set up, you could still potentially damage the gate of the FET when shorting it to ground to discharge it if I understand how its hooked up correctly.
Ideally you would use some kind of FET driver with a voltage source (e.g. linear regulator) to turn on and off the gate plus the gate resistor.