Factory Reset

it is recommended after an update especially after a major OS upgrade

not every time it way better to go safe before any thing happens

when everything is running smoothly no need to reset

i dont think its a good idea to reset your phone often or after any major OS update. If you are experiencing annoying bugs or glitches making it hard to use phone i think thats the time to go for factory reset if it is unsolvable via softwares or antivirus we have on phone. Remember keep factory reset as the last option to fix things like this.

I will do every 3 months once.

mene to jabse note9 liya takse 1 bar bhi reset nhi kiya mst chalta hai

its upto you, how often you want to reset your device. I do reset my phone on the start after unboxing and then use it and next after 2-3 month of use or sometimes when my device lose its smoothness. So its your device and you have your own choice to do so, until and unless someone had paid for it...