I don't think it is anything to worry about. As long as the machine is off (as in not running) and it has been a while since you turned it off (like, maybe a minute), it should be safe to remove it. SD cards, as someone else said, are "hot swappable" meaning you do not have to go through the "safe eject" step. As long as it is not being written to, read, or whatever, removing it is safe.
I would think, given the delicacy of electronics, it would be more of a risk to plug and unplug the machine each and every day!
If you wish to unplug, then unplug from the wall, NOT the back of the machine.
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