In the back of one of the manuals for the Civilization computer games - I forget which one - there's a section that talks about how the game was designed. This contains a nugget of wisdom for game designers of any stripe: "If something isn't working, double it or halve it."
I think that this principle is a very sound one. Suppose you have a situation like "The penalty for juggling while skateboarding isn't high enough - nobody feels its that difficult in game, though everyone agrees it would actually make it quite a lot harder in the real world. Plus the guy who can force people to skateboard feels way underpowered because putting people on skateboards is barely impacting their juggling at all."
It might be tempting to increase the penalty by one and see if it makes a difference. The problem is that playtesting tends to produce a fairly limited set of data points, because of random variance (Even if the game has no randomness the skill of the players you have is a factor and even if you are testing with the same players over and over they will have good days and bad days). It's fully possible to have an experience where something is weak, so you make it more powerful and then to play a half dozen games in which it does even worse. Just by chance.
So to actually see the difference there's a sense to making big changes. We'll not increase the penalty by one - we'll double it! It may well be that doubling makes it waaay too hard to juggle while skateboarding, but if that's the case you know the undoubled variable was a little too small and doubled was far too high and that gives you information to pick the right point in between. Compared to the very real chance of learning nothing with a one point bump, there's a good argument for doubling.
The thing about doubling is that you really have to understand where your zero point is.
Imagine two systems for a game.
In system A I roll D6 + 3 and need to get a 7+
In system B I roll D12 + 3 and need to get a 10+
The chance of success in both are the same. But if (for whatever reason) we double that +3 then they change a lot. I don't know about you, but I'd be super confident of rolling 7 or higher on D6+6.
The trick is to understand what doubling something actually *is*, specifically it's making it twice as big relative to zero. However in our first game zero is clearly not the default state, presumably when we set the target as "7+" we anticipated that under normal conditions the player would have some sort of bonus to the roll. Perhaps in the average situation a player has +1 to this roll - in that case we should treat that average case as zero and double relative to that. So when we want to double our +3 modifier rather than doubling the number itself we double the difference between it and the zero point, making it a +5.
If you're feeling fancy you could look at the ratio of success to failure and aim to double that rather than doing anything with the raw numbers. D6+3 will have a ratio of 1:1 between successes and failures, so we might want to double that to 2:1, which means wanting a 66% chance of success. That means we want 3/6 sides of the dice to result in success and so can make the modifier D6+4 - it turns out that the random factor and target numbers we're working with are sufficiently small that in this case a one point bump does make a big enough difference!
I've been doing a lot of this with Genesis recently, having built up datasets to the point that they show me which things it's great to be a god of (Fire, Showmanship) and which ones tend to lead to failure (Madness, Undead) I wanted to make a new version to rebalance things. However it takes a *lot* of plays to get a decent amount of data for Genesis since a lot of the gods aren't used in any given game so keeping the number of iterations down is important. That means adopting a policy of making significant changes that are going to show enough of a difference to meaningfully drive decisions, but doubling the level of a card in this game isn't something that makes sense. A card is level 1-10 so fully half of them can't be doubled without extending the range. It's been better to look at "How many other cards in the game will this beat" and to aim to change that number significantly, though of course changing any card slightly changes that number for every other card
The point is that while doubling a thing feels dramatic making big changes during testing is healthy. You learn more than small changes and sometimes it turns out that a big change is what you needed and you can keep it as is. The rule of "double" isn't necessarily important so much as the overall philosophy, but if you do want to keep it the trick is to be mindful of what you're doubling and relative to what zero point: Raw numbers often don't tell the whole story.