Defragmenting the hard drive on your desktop or laptop should be done occasionally, as it will increase its performance. The same is not true of the SSD or eMMC in your tablet.
Defragmenting the internal storage on your mobile device won’t speed it up — it will have no effect on performance and will actually reduce the tablet’s lifespan.
When computers save files, each one isn’t always stored in a continuous bunch. Bits of them are broken up and placed wherever there’s room. Defragmenting brings these files back together, which increases the speed at which they can be read … if you’re using a spinning hard drive.
More expensive tablets have SSDs (Solid State Drives) while cheaper ones have a slower eMMC (embedded MultiMedia Card). For either of these, there is no slowdown for the computer to pull up the various pieces of the files because there’s no read/write head moving around on a spinning platter. So defragmenting accomplishes nothing.
Well, not exactly nothing … it does lower the useful life of the drive.
Each sector on an SSD or eMMC can be written to a limited number of times (about 2,000 to 3,000) before it is worn out. When a drive is defragmented, just about all the data on it is accessed, erased, and rewritten somewhere else, often multiple times. It’s sort of like compacting months of use into a few minutes.
With normal usage, a tablet’s battery is typically worn out and the march of progress has made the device an obsolete relic before the internal storage begins to get significantly worn out. But defragmentation is not part of “normal usage”.
So don’t do it. There are no benefits and it’s genuinely injurious to your tablet.