If your tank is cycled, adding another filter wont make it more cycled. You will still end up with the same amount of nitrate produced by your cycle. But there are plusses to running 2 filters.
The additional filtration will mean your tank can cycle out more ammonia. So, you could stock more heavily with the additional filtration. However more ammonia leads to more nitrate which would mean more water changes.
If one filter isnt sufficient to cycle out all the ammonia then adding another filter will help.
A 2nd filter will help with mechanical filtration, the additional filter should do some work removing particles from the water.
A 2nd filter will give you some capacity for chemical media should you need it.
2 filters gives you redundancy. If one filter fails and you don't notice for some reason, the other will keep running and provide filtration.
Filter maintenance and cleaning can kill off some of the beneficial bacteria responsible for your cycle. 2 filters and alternating maintenance minimises the impact of cleaning and maintenance on your cycle.