Does DIBS benefit buyers?

I RECENTLY went to a SOHO launch where the developer offered a 10% rebate and DIBS (developers’ interest-bearing scheme) package. With regards to the rebate, 10% of the selling price will be waived provided the sale and purchase agreement (SPA) is signed within a certain period.

I understand that the rebate is not included in the SPA and is only given upon vacant possession. This looks unfair, what happens if there is no “vacant possession” where the developer does not complete the construction?