If you're gonna game, then do it efficiently. That's my motto at least :lol:
To game on a laptop with ultra graphics you will need to spend much more money than you would on a desktop. So if you're on a budget a desktop could save you sometimes even half the amount of money you would pay on a laptop or mac.
Laptops are very susceptible to overheating and that is a no-go when it comes to gaming. They will generally give you more issues, and will be less powerful for more money.
Another thing that I personally felt was that buying a desktop was a good investment. I bought it only to be able to play on ultra settings but I thought I'd spend an extra 200€ on buying something extra powerful. Now I know no matter how many packs I buy or even if the Sims 5 comes out and I want to play it, I will likely be able to with no issues. To do this on a laptop I'd have to spend double the amount of money and then still wouldn't be sure it can handle the next generation Sims games.
In my opinion the only reason to buy a laptop is for mobility reasons. In every other way a laptop will be inferior than a desktop.