They are usually people who are PvP. They need all the possible stat points in order to maximize other areas; vitality or dex usually.
However, now with the annihilus around, and other gear with + all attributes (shako, maras, azurewrath, all botd's, etc etc), you can really think about the armor you are going to have enigma in. I personally have a superior mage plate enigma, with 1025 defense, and 55 str required. Dusk requires 77 str (or 87, not sure) which equals 22 more vitality, when combined with battle orders, is ** more life. Archon requires 103 str, which equals 48 vitality, when combined with battle orders, is 192 life. Ofcourse if you used these extra points in dexterity your blocking would increase considerably.
I personally have 29 base into str, with 19 stat anni, 5 stat shako, and 2 stat maras, gives me 55 strength. From there, enigma kicks in, then I can wear homoculus, trangs gloves, marrowwalks, etc etc etc.
Even though i dont pvp, i didn't feel like wasting points when i didn't need to. It is a hassle to wait until lvl 70 (lvl requirement of anni charm) but it is well worth it when you realize how perfect of a character you have made.
Edit: I personally think an Enigma Breast Plate is the most moronic thing to do with such valuable (although probably duped) runes. Breast Plates = 30 str, however only give a maximum of around 850 defense. Enigma Mage Plates are 55 str, and can reach around 1050 defense. With the type of set up I have, with 29 base str, I have an armor with 200 more defense that was easily equipable.