Index.dat files and CCleaner

From what I understand, though CCleaner can delete the index.dat files upon rebooting they are immediately recreated. If this is the case, what is the purpose of deleting them? Does it achieve anything or is it futile?

And is there a relatively easy way for people like myself who lack a great deal of knowledge about computers to delete tracks like those contained in the index files safely and permanently? It's kind of concerning considering my bank information and such could be accessed fairly easily by someone with a mind to do so the next time I need to bring my laptop somewhere to be repaired.