The mainbenefit is it has a finite time frame for filing lawsuits upon completion of the EIR. As pointed out above, lawsuits can delay projects for years sometimes.
I guess my only problem is with it being upon completion of the EIR as opposed to earlier in the process. For example, let's say the EIR gets completed next July. If they have 2 months or whatever to file then they can take it right up until September. At that point, if a judge rules that the lawsuit has merit and it goes to trial, there's no telling how long the trial would take and if it takes too long, it may go past 2015 and make it impossible to meet the league mandated November 2017 deadline.
OTOH, if they force them to file within 3 months of the start of the EIR process, everything can be taken care of legally a few months in advance so that when the EIR is done, they can start with demolition and ultimately, construction of the arena. My thinking is that the lawsuits have nothing to do with the EIR itself but rather what will come assuming there are no red flags, in this case being the construction of the arena. Therefore, I don't see why they don't make them file during the early stages of the EIR process.