It allows the Lib Dems to foam at the mouth in public.
As to which, am I mistaken in the following understanding of the LibDem proposal.
We negotiate whatever we can. Everyone thinks this will take longer than two years, so anticpating many provisional agreements, but hey ho.
we get the result of the negotiations and put them to teh people in a second referendum. The people then decide.
There are possible real difficulties with this.
The article 50 notice provides that if no agreement has been reached on the second anniversary, we are just 'out'.
The article 50 procedure makes no provision at all for a change of mind. it is an explicit fundamental of the recent Supreme court decision that the notice is irretrievable, and it is exactly and only because there is no way back, that Parliament can only have a 'significant' say so by having the right to vote against the Bill now before parliament before the Article 50 notice is issued.
It has been said that EU realpolitik will overtake the letter of the law and allow us to change our minds. What possible justification can there be for that as a basis for proceeding?
If we proceed on that basis, will it not exactly encourage the EU to make the deal we are offered impossible of acceptance?
If the proposed referendum results in an answer 'No, we do not want to leave.' what mechanism do the LDs identify to halt what Article 50 says just happens.