SD cards have been in the market for sometime and I must admit there handy devices and you should always include one with the purchase of a phone and here is the reason why.
Manufactures recently started noticing that they can make more money by charging you data space on the cloud. So if you have taken pictures or video's on your smartphone. You phone has special apps that stores them in the cloud so that your phone will never run out of memory, which is good. The bad is that when you run out of memory in the cloud, now your forced to purchase more space and manufacture's love you even more.
Now by installing an SD card you eliminate the extra cost of the cloud monthly and your overall savings will be in significantly less than if you had stuck with your manufacture to purchase more storage.