The cracked skin that you may get at the back of the heels may be a painful problem if it is allowed to progress. This problem happens when the skin around the backs of the heel is dryer and thicker than it should ordinarily be. When the callus increases to make that dry thicker skin, it simply splits because it is not very supple or adaptable. The split that happens in the hard skin, then tries to tear or rip the normal skin below it. In the most severe cases, this will become painful, may bleed and be an for an infection, so does need to be given serious attention. The explanation for these cracked heels is not totally clear. Many people simply have a tendency to have a dryer skin and some people, due to the way that they walk tend to build up the callus around the sides of the heel. Being overweight can be another risk factor for this. Shoes which are open at the back are also considered to play a role in this problem.
The best way to manage the cracked heels is to find an expert podiatrist to get rid of the thicker hard skin and then use an cream to make softer the rest of the skin. You could try and get rid of that skin yourself with something similar to a pumice stone or file, but that's a lot of work and needs to be carried out a lot. The emollient lotion used after this should be put on regularly to help keep the skin well moisturized and flexible. There quite a bit of opinion of what's the most effective cream or emollient to use is and the best answer is the one which suits your skin. Some trial and error may be needed to get the best one. For cracked heels most foot doctors usually advocate starting with a urea based emollient.