One way to handle tables whose size is not known in advance is to make them fixed,

Question:

One way to handle tables whose size is not known in advance is to make them fixed, but when one fills up, to replace it with a bigger one, copy the old entries over to the new one, then release the old one. What are the advantages and disadvantages of making the new one 2 × the size of the original one, as compared to making it only 1.5 × as big?