The only benefit is If they sign I can use customer names instead of generic descriptions (e.g. "large bank" or "telcom provider") and I can show product interfaces.
Personally I thought an optional NDA strikes a good balance, but I've been surprised at how many candidates just sign NDAs automatically. We communicate that it otherwise has no bearing on their application but I suspect some believe that it'll increase their odds.
Enforcing an NDA is more difficult then a lot of people think. If you have a legal department you can threaten to sue an individual for anything including breach of an NDA and in that sense it can be effective. But the only times an NDA has been enforced in my working experience is when there is real theft of intellectual property and you don't need an NDA to prevail in that situation.
https://www.acc.com/resource-library/issues-enforcing-nondis...
Apart from this reference nonsense asked right in the first form - refused of course leading to exclusion by some automation immediately - I met with ability test of rapid finance related calculations - not enought time to complete all and only tests how good I am in finance tests having a non-relaistic idealistic scenario as a context - for an engineering position - which then "will be the baseline for promotion decisions" later. Refused to take the test, then I was refused too. All this after successful engineering interviews and conceptual agreement on particulars (salary, location of work, start date).
Not remembering I got refused and calling me with the same kind of position in couple of weeks, greeting me with "you have experience that fits perfectly" just to offer me something require experience I don't have so obviously not reading the long forms they mandate to fill in down do the last dot, and similar clue and careless aproaches are what I experienced.
There are dozen or (famous in their field) organizations I could discourage people from applying to due to the dumb procedures even on the most elementary level. Frightening what could go on there concerning organization and administrative tasks.
All have very cutting edge approaches to forming a perfect work environment that they consider the utmost importance if you look at their career pages with explosively happy all young and dynamic and diverse and smart and pretty people. They are full of bulls..t and they know that (or hopelessly clueless which is equally frightening).