Is there any chance or situation I will have to connect an electric piano or electronic drums through a DI box with my UI24R mixer ?
DI's task are
1. Impedance conversion from High ( Kilo ohm or Meg ohm ) to Lo ( hundred ohm ).
2. Unbalanced line to balanced line conversion.
3. Level reduction ( Attenuation ) if it had the PAD.
4. Ground lift or any metal isolation by using transformer to avoid noise, if it had this function.
You don't mind about impedance for those electric instruments because they are already low impedance.
And those instruments have output volume knobs.
So the situation you need DI is limited.
If those instruments does not have the balanced outputs, they will be connected with unbalanced connection.
If the length among the Mixer and the instruments were longer over 10m, balance connections usually get to necessary against the noise. Balanced connection can avoid some out-coming noise. Unbalance can not.
If it did not get much noise there, or you did not mind the noise fortunately, you can connect them with unbalanced connection even if you set them in 100m distanced places. Normally such long unbalanced cable gets some noise from ground or radio wave something.
There are some devices to lift the ground or isolator instead of DI.
Actually only some DI have those functions.
Actually it depends.