"I don't really see the justification for undertaking otherwise unnecessary debt."
Personally, it's not a path I'm greatly a fan of, or actually following myself. But I can see the justification for it.
As you know, there's an increasing number of geared property (and indeed geared equity) investments out there. This is really just another one, with higher levels of gearing available, lower interest rates available and no Capital Gains Tax on exit.
If someone could happily live in a €300,000 house with a 90% mortgage, but can afford to, and does buy a €400,000 house with a 90% mortgage, effectively they're buying a highly geared investment of €100,000 in Irish residential property for a stake of €10,000. Interest rates on the borrowing will be very low and no CGT on exit.
As I said, not my own cup of tea, but I would hold it in higher esteem than some of the other geared investments on the market today. An awful lot depends on your personal view of the long-term prospects of Irish residential property and your appetite for risk, because everone (I hope) knows that gearing multiplies downside risk as well as upside.