I print the same objects over and over. I use hardened steel nozzles. My last 20 rolls have been GST3D which works very well, is very hard and strong and $12/roll made in USA (Miami). This gives me good testing with minimal variables. I discovered that my prints would gradually degrade and by the end of a roll results were poor. I found that the nozzle would gradually have it's diameter get smaller as printing progressed. A simple test was to do a filament load @ 210C. I found that a brand new nozzle would give me an extrusion of .75mm to .85mm. My prints take 11 to 14 hours and I began the practice of doing a filament extrusion at 210C and checking the diameter of the extrusion. I found that after 14 hours there was always a reduction in extrusion diameter. So I would pull the filament after filament load and and use a 0.4mm needle to re-enlarge the nozzle. Now when I did an extrusion I would get over 0.7mm diameter. Eventually the enlarging holes ( 10 rolls worth) would not bring me over 0.65mm diameter. This is the diameter that I found starts giving reduced quality prints. I took these nozzles off to figure out what was going on. I cleaned them and made sure the 0.4mm needle passed through the nozzle. Did not matter, the nozzle would not extrude past 0.65mm. Answer: Do a filament load fairly often. If the extrusion is less than 0.7mm replace the nozzle. This has always restored the quality of my prints. You can extend the life of the nozzle with a 0.4mm needle.