Well, for the last 10 years at least, I have been saying that you do not need a primer to spot prime patches. I have also said that using an actual primer can be a bad choice to spot prime with because those spot primed areas can flash. This would be due to the primer doing a better job at sealing (or worse) than the actual paint does so those areas that are more sealed will look different in critical light (like when you have a window casting light down the wall). About 8 months or so ago, I did a huge job for very picky customers with BM's Regal eggshell and one of the rooms was a well lit foyer with high walls and lots of critical light. I painted like I always do and had huge issues with patches flashing through. I spot primed all my patches twice (with the Regal eggshell) and then double coated all the walls and I was still having problems. I complained to Benjamin Moore and I think they gave me a refund and allowed me to upgrade the remainder of the job to Aura at the Regal price. Since then, I have had flashing problems with both Regal and the newer Regal Select lines and really Aura as well. So. I will no longer be claiming that you do not need to use a primer. I don't have these flashing problems with Sherwin Williams Cashmere...that's for sure. I will say though that if you want a perfect paint job, prime the whole wall, not just where there were patches.

Also, primer is no longer made? Come on. Primer will always have it's place, especially since primer like Zinnser 123 is $15 per gallon and most decent finish paints are $45 per gallon or more.