Former SQF Auditor, Present SQF Consultant, soon to be an owner of a food company...
I do not see any value in doing no notice inspections.
I did these when I worked as a hotel inspector for Ramada and Howard Johnson - I find them to be very confrontational regardless of whether they were a good operator or a bad operator - the only good purpose was if they were a borderline operation the no notice inspects would normally result in failures and getting these hotels booted out of the system.
I find many parallel's between the hotel/restaurant and food industry - while the food sectors have to adhere to GFSI scheme codes the hotels/restaurants that I inspected had to adhere to franchise codes - the major difference is the hotels were compliance audits, where there are many grey areas with SQF, BRC, FSSC, etc - and are in effect compliance, but not like the hotel chains.
No matter how you look at it, an operator knows when the inspection is coming and with a no notice they still know there anniversary is coming up and it might be 30 days this way or 30 days that way - so the borderline operations are kept on their toes only when they get into the window, while the good operations are humming along all year long and see a no notice inspection as another set of eyes and actually enjoy the process.
Lately however as a consultant we are getting lots an lots of feedback from our clients of extremely confrontational episodes and its not coming from the company side employees but from the Auditors.
Mostly an inspection is not exactly an enjoyable time and having spoken with a number of Auditors they hate doing unannounced inspections as well - I remember doing inspections in hotels on no notice and had to sit in my room (we would stay on property the night before - we'd do the guest impact part first before announcing ourselves at the front desk in the morning) and build up strength to get thru the audit.
Seriously, low courage Auditors, or Auditors that get intimidated easily crumble with many an unannounced audit.
Here's an interesting story, my boss in the hotel franchise company had been a Manager at a Holiday Inn. At the time Holiday Inn had a fleet of cars for the QA inspectors with their logo's all over the cars - there was a toll plaza about 5 miles from his hotel, he had talked to all the toll takers and would give them 2 nights with all meals, etc at his resort property if they would call him as soon as they saw a Holiday Inn corporate car come thru - he was a good operator but it gave him about 15 minutes for all department heads and exterior grounds personnel to touch things up quickly, or excuse certain employees to go home that could cause issues.
With the quality of the auditors out there today, I find the opportunities for problematic confrontations has gone up greatly because of these unannounced audits.
Rambling done, back to reviewing 3 unannounced audits!