I don't disagree that a NDA is vital in a sale process and this article explains the needs and merits of a NDA well. 

Much of the focus on a NDA is around non compete clauses and non solicitation rather than the actual use of information elicited during a sale process. I find this strange.

I have regularly debated whether a NDA signed by other bidders helps the ultimate purchasers.

How many times does the ultimate purchaser ask the sellers for a list of the people who signed a NDA? How often are non successful buyers reminded of their obligations post deal? Rarely is the answer to both questions. 

In a well run auction process information is shared with potential bidders. Sometimes a VDD ( vendor due diligence) report is prepared both covering financial aspects and also legal issues of the target business.  Much useful and business sensitive information can be gleaned from these reports.

While some  details considered  very business confidential by a seller or sale adviser get redacted initially (eg pricing in contracts), I am often shocked how much information you can uncover in other documents in a data room which has been redacted elsewhere.  

Increasingly, we are also seeing clean rooms to get round the issue of competitors seeing too much. This involves advisers having access to information the bidders don't see.  Advisers then report back findings to their clients. While this is better than giving access to all bidders information which the ultimate purchaser may not want the failed buyers to see in practise,  I again have been surprised how relaxed some sale advisers are about the way clean room information is communicated. I put this down to sale advisers chasing the deal rather than always protecting the ultimate buyer's position. 

Many clients are quite sanguine about auctions and information being shared but I believe a failed bidder could obtain a significant commercial advantage which can help their business in the future even without ultimately buying the target. Successful bidders need to recognise this in their deal appraisals and during post-deal integration and consider reminding failed bidders of their obligations they signed up to when they entered into the NDA, often many months previously.