Last January I resolved to not buy any games on sale. I mostly stuck to my resolve, although I ended my resolution a bit early. I bought more new games, mostly for consoles, and I did play the games I bought. When I got a PS4, I allowed myself to buy three games on sale, but I've only extensively played one of them. The games I impulse buy are rarely ones I devote much time to playing.
If you have the luxurious problem of having too many games to play, and you find yourself impulse-buying a lot of games, I recommend not buying games on sale. When you invest more money in a game, you feel more obligation to actually play it, and hopefully have fun and feel some fleeting sense of "accomplishment". But if you don't have a lot of money to spend on videogames, definitely shop the sales (and remember that Nintendo rarely puts Pokemon/Mario/Kirby games on sale)! I didn't buy any humble videogames bundles this year and at first it felt like I was missing out, but I actually didn't miss out on much.
Here's some helpful self-talk for talking yourself out of buying more videogames:
"If it turns out I really want that game later, I can buy it at full price."
"It's not saving money if I don't play any of the games I buy."
"When will I play this game?"
I pretty much stopped buying games in genres I don't actually play. As interesting as the FPS genre may be, I don't like the gameplay. I also tend not to get into strategy videogames. I like visual novels, but I only like to play one at a time. I think I have way more platformers than I'll ever play. Basically, I have enough videogames, and the main reason I buy more is to feel like I'm a part of the gaming community at large. But that also means that the games I do play tend to be things like Pokemon or Final Fantasy XV. I like the idea of playing hipster videogames, but I'm such a snob that the only things that draw me to indie games are really cute art or unusual storytelling mechanics--like Pony Island.
I also think a helpful rule for me would be to play games within a week of buying them. When I can still remember what the game was about and why I bought it, I feel more excited to play the game. There is a certain charm to "discovering" a game you've owned for a while though! I know I'm not the only one with this problem. Do you consider spending $8-$15 a month on games you won't play to be useful for the thrill of shopping? Or is it more efficient to spend $40 every few months on a title you're hyped for? My rate of videogame consumption is pretty low, so I think my current system is working well for me.