Steam offers a wide range of deals and price cuts, and they do so throughout the year. While there is a potential gain to wait until particularly periods of the year, such as international holidays (like Christmas) for the really low prices, every other week there will still be price cuts of up to 80%. On numerous occasions there have been paid-for games that have been offered for free, as a special promotion.
One of the biggest and best features of Steam is that it gives you a rundown of all of the current deals whenever you log into the platform. This means that they have virtually eliminated the requirements for bargain hunters to spend hours searching for deals on new games; they are all organised and clearly advertised.
On top of steam deals, there are also a number of other deal providers on steam games. Usually these operate as charities; game developers donate a game to one of these charities, who are then allowed to sell it on the games developers behalf in return for charitable donations.