There is typically no reason to upgrade the firmware when it comes to HIK. Typically with technology you get "additional features" with firmware changes or patches to address "security matters".
However, HIK is notorious for taking customizable features and locking there product down more with firmware upgrades which is why most don't even want to do them. Bottom line most will tell you "I want to upgrade firmware because "i can"" However, as most cited below, if it works when you get it, don't f* with it.
Now, with that said - I'm a fan of private label HIK products located here in the US, and I personally choose to pay $10-$30 more per camera depending on model to get a US HIK camera that is firmware upgradable and includes a 3 year warranty vs something from ali/china that is not firmware upgradable and carries NO warranty support - especially when HIK won't even support it or help you.