From a financial management (as well as a credit scoring) perspective, the less cards you have the better in most cases. It is easier to organise and keep an eye on your finances, and is also more secure since you only have one card to keep an eye on. This almost contradicts the adage that you should always use a credit card with a specific purpose in mind.
But a balance transfer and purchase card can fulfill two requirements at the same time, in a cost-effective way.
Balance transfer cards allow you to take a debt that is racking up interest on another card, transfer it to a new card for a fee, and avail of a lower rate or zero rate on the new card for a period. This can allow you to start paying down the debt without the charges and fees continuing to increase.
A card that offers an arrangement like this enables you to make purchases (within a limit) and not have to pay any interest on the amount for a set period. This can function like a very cheap (or free) short term loan. This kind of offering is very useful for big purchases such as a new computer. It’s worth remembering here that the payment protection offered with credit card purchases is one reason to use them for spending like this.
In many cases, you can get a combined credit card card that offers both these benefits in one. For example, you could avail of one of these cards and transfer a debt that is incurring interest on another card, and also use it to make a big purchase like a new fridge. If you are certain you can pay the transferred debt, the cost of the new purchase and the balance transfer fee within the interest free period, you have essentially taken care of an old debt and got an interest free loan for a (payment protected) new appliance in one.
There are of course fees associated with balance transfer, usually a percentage of the amount transferred. Furthermore, since a balance transfer and purchase card has such handy benefits during the interest-free period, you could be facing steeper charges and fees if the balance is not cleared within that period. It might be the case that having two cards for the different purposes allows a better deal overall.
Look into your financial plans and what your requirements are, and then see if a Balance transfer and purchase card would suit you.