LTD, in the UK anyway, means "limited liability" - ie specific to that organisation only. In a group scenario that means that if an LTD went bust, the administrators/liquidators could not pursue any other companies within the group for settlement of debts owed by the one that went bust if it can't cover them itself.
Similarly, a sole trader could lose everything they have - their house, car, life savings.. and not forgetting the cat etc, if unable to repay debts as they fall due, but if they set up a Ltd company (quite cheap to do) and operate through that, then they'd only be liable to the extent of equity in their Ltd should it all go wrong.