I've thought about replacing the internal HDD with an SSD to improve speed of the console and especially loading times of games. After I saw good youtube reviews of people using external SSDs attached via USB 3.0 I changed my mind and I added also an external SSD to my Xbox One S. I used "Samsung Extreme 500" SSD with a capacity of 240 GB (which is working fine even it shows only 230 usable in Xbox menu). Speed has increased! :-)