Is it worth waiting for winter sales or flash sales?

It's not really one or the other, it depends what you're looking for. Winter sales are more reliable if you need specific stuff - you know what you want and you'll usually find it cheaper - but that's also when everyone's shopping so it can be a pain. Flash sales can save you money overnight but you gotta be ready to jump on it fast and you don't always have exactly what you need available. Honestly, the main thing is not to buy just because it's on sale if you don't actually want it.