It will save you money in doing what you propose.
Let’s say for example that you have two credit cards A and B, each of which you owe £1,000 and are paying a hefty 20% interest p.a. 20% on £2,000 equals £400 interest a year – or £200 per card (or about £100 per card over a 6 month period).
Now suppose each card is offering you 6 months interest free balance transfers (for a 3% fee). So you transfer £1,000 from card A to card B. This will cost you £30 (3% of £1,000) – Card B now has a zero balance, and card A has £2,000 owing, for which you are paying 0% on £1,000 and 20% for the other £1,000. You now transfer £1,000 from card B to card A. The net result of this is that each card has a £1,000 balance at zero % (for 6 months), each of which has cost £30 (total £60), saving you around £140 over the six month period.
An important condition of each credit card is that by its terms and conditions, the higher percentage credit must be paid off first. I believe that this is now a mandatory condition for UK credit cards – in the past, cards paid off the lowest % credit first.
If at the end of the 6 month 0% interest period – you can find another card supplier offering 0% for a 3% fee – then you will have reduced the interest paid on your credit cards from 20% p.a. down to around 6% p.a. saving you around £280 over the year - in the above example.