The biggest perk for me for a dedicated NAS is redundancy and hot swap ability.
It is inevitable that a few of your spinning disks will die and need to be replaced, a proper dedicated NAS box will let you pop out and swap that drive and then the NAS software will rebuild the array for you with no data loss.
Obviously you can do most all of this with a normal desktop, but it's generally easier with the right hardware.
I custom built mine running Truenas which was way cheaper then a dedicated NAS, but also I'm an IT turbo nerd so I wanted to do the whole thing myself.
I mean you can always use the web version of office for 'free" with a Microsoft account. There's a 100% chance your paper gets used to train AI but still