Optimum means the best amount for your needs. For storage, whether SSD of HDD, make a rough computation of how much storage you will need and buy just the optimum size for your new computer. Don't fall into that trap that you need 500 GB and that it can last for only a year so you are going to buy 1 TB instead. But if your need did not fill up the 500 GB limit then you are losing some money on that. Besides, a bigger storage is more prone to problems aside from the added time in accessing the data.