One of the most important things to consider is whether or not what you're doing is going to produce any incremental benefit. Let's take the child tax fitness credit. The goal of that was to increase the number of kids in athletic sports. What we do know from the evidence is that it has had no discernable impact on the number of kids participating in sports. It is instead subsidizing parents who are already putting their kids in sports.
If the vehicle itself doesn't deliver on what is a very admirable policy goal, then it isn't the appropriate tool to use to achieve that goal. In that case, subsidies toward low-income households, or at least toward supporting reduction in fees of low-income households to participate in sport, would have a bigger incremental effect. It induces those households to enrol their kids in that sport because they get the benefit right away. They don't have to wait a year or a year and a half after they have enrolled their child to get the money back from that expenditure.
I wouldn't say there's a carte blanche rule. It's this matter of what you are trying to achieve and whether the tool will achieve that. In most cases when you're looking at incremental benefits, if you're trying to get more people doing something, the tax credit isn't the way to go.