I did some checking using the i app. It shows around 214 MB of memory and 53+ MB of "Disk" in my 64 GB iPad. That is right after startup after doing a total shutdown. After a few hours with the same level of inactivity, it shows 163 MB of Memory and the same 53+ GB of Disk. Reboot and the 214 shows again. So we have some form of Memory leakage and it probably helps to reboot at least once per day.
This may be caused by poorly designed apps although I thought Apple had that under control. Evidently not.