Some devices don't support that function, but you don't say what device you have or what OS version it's running. For those that do, it's still not recommended for several reasons and not all apps will support it either. Apps will load and perform slower and it simply doesn't free up as much space as you might think. On top of that - apps that are moved to SD will move back to internal storage when updated. You're best off moving your pics to SD and if that doesn't free up enough you may be better off just trying to find a device with more internal storage.
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