What I'm referring to is how in doujins, manga, and visual novels especially, the main character has practically no personality either physically or intellectually so as to make it easier for viewers to pretend that they are that character. This can be done in a variety of ways such as using the character's POV as the default perspective, giving him very little in terms of unique hairstyles or facial features, or straight up erasing his name and face all together. It is very common in harem genre works as well. At its lowest level, it is an author simply dedicating more work and resources toward the heroines because it seems to matter more. At its highest level, it allows complete customization of him as an avatar that you are able to make all decisions for and shares your name.
This doesn't have to be porn-related either. First Person games usually try and communicate this as much as possible for immersion. The Zelda games always let you set your name at the beginning.
I've always thought of this concept to be more off-putting than inviting, at least when done wrong. When done right, like when operating at the higher levels of it, the distinctions between you and your character in a game end up being rather transparent. When it's at a low level, sometimes the character makes up for a lack of facial features with a better inner personality that can show that their actions, rather than appearances, are what make him a likable person and lucky with the ladies.
When handled wrongly, your avatar's actions are always being chosen linearly and it feels more like a movie from someone's eyes. The character with no redeeming physical qualities also acts like a douche that all the girls like for shitty, if not arbitrary, reasons. He never takes initiative in his relationship and has those scumbag tendencies that makes you worried if he really would happily accept a kiss or boob rub from someone that's not his partner.
So what do you guys think? Is it that big of a deal that the MC not have any decent features? Maybe you find it a good thing to easily reach that state of projection.