I guess I just can't suppress my contrarian nature!
Threads can be worn out by improperly screwing things in and out. How hard is it to do carefully and correctly? I always remove the nipple to clean and always remove any "clean out screws" as well. They both get antisieze when put back together. The only barrels I own that have corroded in place "clean out screws" are a couple that I acquired used. So does that corrosion continue? Will they eventually blow out due to corrosion? I'm not sure. But I am sure that the ones that I remove, clean and lube aren't going anywhere.
And, "yes", I know how they got there and why. I know they aren't there to aid in cleaning but they are there and IMO need to carefully removed and the threads kept clean just as is needed with a nipple.