when I first started playing DQ, I discovered Set Affixes on the Legend items. they were hard to use, at least for me they were, and I didn't really use them much. but now I am on my third Farming Build, and I am tweaking it a lot to keep it going until I can replace it with Golems Ultimate Farming Build.
now, when I was Ascending, I wasn't using any Sets, until I got past Perk 4. then I added Plagued and Adventurer. they helped, but my Ascending build didn't really have room for Sets, but I only needed to get lots of experience, and you don't really need Set Affixes for that.
at this point, my current farming build has Equality, Ascendant, Arcanist, Pathfinder (pet), Demonic, Electrocution, and Adventurer. I only have Adventurer because I am trying to get another Set, but ran out of crystals.
now, while I was trying to get another Legend affix, I got a Sprint Proc, and I thought about doing the Jasper trick to get Momentum set, so that I can get another damage boost going for the build I have.
the funny thing is that when I first made this Third Farming Build, I had no room for Sets, but I ended up making room for them so I could keep climbing up to floor 500 and beyond. I just added Sets one by one as I climbed.
the hard part was figuring out which Sets to keep and which ones to drop, and am now at the point I need a Set or 2 from other classes.
in addition to all the gold, CS, and MS I spent to keep this Build alive, I have been learning about how the different Sets work, and been getting ideas for future builds.
one thing I have learned is that Set Affixes are a lot like Crystal Affixes. most Crystal Affixes are triple the amount of the Epic Affix they replace. Set Affixes give from 1-3 bonus's that are increased by how many of the same Set you have on your items at the same time, and some Sets have a Set Bonus that give a bonus if you meet the requirements.
and finally, when you are just starting to play DQ, you might only be able to use one or a few Sets at one time, but later in the game, you can be like a pro, and have a lot of Sets powering up your gear. your build might not need Sets on all your items for the build you have, but some builds do. so put a Set Affix on your build, and watch the monsters melt away.