If you use version 1 or 2 I recommend using Vae, if you use version 2.5 it is not necessary to add it
A merge of some of my favorite models
V1:
XlAnIL x NooblyAI x Better Days [Illustrious-XL] x WAI NSFW Illustrious V9
V2:
XlAnIL x Better Days [Illustrious-XL] x IllumiYume x
WAI NSFW Illustrious V9
V2.5:
This version has Vae integrated unlike V1 and V2 which do not have it.
(The difference of V2 from V1 is that version 2 is more "Screencap" style than the first one)