Overclocking can have it's pros and cons, however I'm not an OC expert by any means and usually leave it up to the motherboard tweaking software that comes with the motherboard.
CPU intensive items will see a large boost in performance, stuff like data compression, cpu based video conversion software, distributed computing like Folding AT Home will all see boosts in performance.
Increased heat output from the CPU and any other component you've OCd requiring additional cooling
Increased power draw
Possibility of introducing corrupted data if the OC is not stable.
Many games will not see a noticeable performance increase when overclocking
Note: I have found the Thermal Interface Material (TIM) within Intel CPUs is absolute garbage especially when pushing the CPU limits. To get around this issue you typically need to De-Lid your processor and replace the TIM with a better TIM such as Thermal Grizzly Conductonaut or another variant of a liquid metal TIM.
Note 2: Using the Liquid metal TIM can be very dangerous to your components if not installed correctly.
Note 3: De-lidding & in most cases just the act of overclocking will void warranties so do so at your own risk.
Note 4: By replacing the stock Intel TIM between the core and heat spreader the average per core temp dropped by 18c at stock speeds
However yes with a Corsair H115i cooling an Intel i7-8700K I'm currently running max speeds of about 5.22ghz with the CPU usually bouncing between upper 3-4Ghz doing general desktop work