Is there a specific (theoretical) reason for using ties or different voices for notes of different length?

For instance this:

[![tied][1]][1]

against this:

[![voices][2]][2]

I understand that if it's literally meant to be sang by two different vocals you'd definitely use the latter. But I'm wondering if you can use it when scoring for a single instrument too?
To me it seems more clear/readable than the tied notes. Well, maybe not in this example, but in pretty complex harmonies or motions it does.


  [1]: https://i.sstatic.net/ie3dQ.png
  [2]: https://i.sstatic.net/6ueId.png