How to explain why it isn't a good idea to shut down a computer using

MeAndMyComputer said:

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For a standard HDD, I try to explain that there is a spinning platter in the HDD and there are "needles" in there that are called read and write heads.
The normal procedure to select shut down allows time for programs to close out properly and for the spinning platter and the read/write heads to come to rest and park themselves safely.
However, using the on/off button everything stops the spinning platter and read/write heads too quickly which can lead to a shorter life span of the HDD and the effect of improperly closing out programs is unpredictable.
If that simple explanation is ok that's fine with me but I'd appreciate some comment or article that's better for me to use.

On SSD's, I don't have an explanation so I need help on coming up with something decent.

You have had some good explanations of why it is important to shutdown gracefully. I'd just like to comment that the heads in an HDD are not "needles" and shutting the power down quickly does not cause physical damage of the HDD or SSD in any way. The HDDs actually use the inertia of the disks spinning down to generate power to retract the heads so no physical damage occurs. As has already been said, a sudden interruption of a write to the disk could lead to corruption of data.

If it is necessary to power the machine off abruptly, if possible, try to do it only when there is no disk activity since disk activity may mean that data is in the process of being written to the disk. Interrupted writes lead to corrupted data which is true for both HDDs and SSDs.