I know its not always possible (maybe someone really needs the gear for a job, although there are alternatives like renting or buying older versions of a lens) but my rule is to never use a credit card in a way that costs me money in interest. Either I pay it off immediately or I use the 0% interest for 6, 12, 18 months (or whatever) deals. The debt is not worth it. There are exceptions obviously but clients don't notice the difference between the hot new mirrorless lens vs the DSLR version that's 1/4 or 1/5th of the price.