Conditional pricing tables don't actually have any effect on the design. With conditional pricing tables you typically are estimating a proportional shift in price rather than a specific value. So you set up an average price, for example, as level 2 of your price attribute, and then level 1 is always a -15% decrease for all products and level 3 is always a 20% increase in price. So your utility model isn't estimating any specific price.
Prohibitions, on the other hand, create correlation in the design and make it more difficult to separate out the effect of, say, a brand change and a price change. If you make Brand A on average show at lower prices due to prohibitions, it's difficult to figure out if someone truly likes Brand A or if they are just motivated by lower prices.
This paper is also a nice resource: https://sawtoothsoftware.com/resources/technical-papers/three-ways-to-treat-overall-price-in-conjoint-analysis