As gustavo40 says.
This is especially worth considering for clothing, with a combination of multiple shaders&overlays.
For example, if you want different colors, length, shape etc, on the outside and inside, when the UV map is constructed in such a way that you can't separate the colors because they're double-sided in one time.
Then the only solution is the method shown in the image above.
Here's an example of an effect from my own experience. (I emphasize that this is a card for Emotion Creators)
emotion_creators isekai Misumi tomoe Tomoe_Misumi tsuki_ga_michibiku_isekai_douchuu Tsukimichi tsukimichi_moonlit_fantasy Uploader: Anni93 Download count: 779 Uploaded on 26/11/2025 1:19:56 pm KK_383518
db.bepis.moe