If you are connecting the pc with your tv using hdmi cable then this is the optimal solution. The pc is much more powerfull than the android boxes.
And dont think that the android boxes as hardware solution vs the pc software solution. Is actually similar solution. And the android boxes is like "not so powerfull pc", with cpu, ram, e.t.c. with operating system. And in that case you install the kodi as program and you run it, exactly as you do with your pc.
So, what are the reasons who make someone to buy a android box, although he or she already have a pc?
The 2 reasons i can think is:
1) A lot of people dont like to see a pc with the cables and the big box into their living room. It dosent look nice and make the room "ugly".
The android box is just a small box that you can hardly see.
2) They want a dedicate box for their tv.
p.e. what going on if you need to work on your pc and the same time some members of the family they want to watch a movie?