POV makes the story more than just a plot
The entire concept of POV is not just a literary convention, it's a slant on how the work is meant to be perceived. Once an author is aware of sub-textual character tools, it's hard to go back to writing simple 'naive' stories about plot-plot-plot.
In addition to wandering through the story like a camera, the MC deepens the narrative through subtext –– there is more going on within the protagonist than just the words on the page and the descriptions of events and things.
reasons to use limited 3rd person POV
Protagonist is an Everyman designed to be the voice of reason, or the barometer of 'normal'. Story is about extraordinary events happening to regular people. The MC is both a witness to the events and a 'regular person' themselves.
Protagonist is a foil to an upside-down crazy world. Everyone else acts irrationally (or criminally) while the MC attempts to set things right (or return to normal).
Protagonist is plot-ignorant or coming-of-age. Events happen in the story that go unexplained to the protagonist, but the reader is meant to infer there is more going on ahead of the MC's knowledge. The reader knows which mistakes the MC is making.
Protagonist is an unreliable narrator. The reader is not a step ahead of the protag, instead the MC is gaslighting, or extremely biased – the discovery of an unreliable narrator by the reader works as a kind of plot twist that changes the meaning of events which could not be told objectively.
Protagonist is a stooge who digs their own 'man in a hole' plot. Reader is meant to perceive the MC as typical of a personality type or a fallacy of thought, possibly exaggerated for comedy/tragedy/parable but also somewhat universally relatable. The story is about 'teaching them a lesson' or softening their personality flaw.
Protagonist is an avatar for the reader and styled to flatter the (presumed) reader demographic, probably being unremarkable in appearance, 'bookish', and naturally skeptical, while also a bit superior in some skills and social perceptions, balanced out by modest (humble) economics and status. The 'plot' is typically their social rise.
Protagonist is a Mary Sue whom all the other characters orbit, acting as simps or antagonists in Mary Sue's universe. The story is 1-dimensional so there really is no other POV of any significance. The difference in an Avatar and a Mary Sue is that Avatars have character balance against their world and their circumstances, while Mary Sues are generally a power-fantasy for the author (not the reader).
In all but the Mary Sue example, the MC serves a meta-narrative purpose for the reader. Characters add dimension and meaning to plot events.
Me in the mirror
I don't typically picture how I look whenever I do mundane things.
Then don't describe the MC.
A third-person narrator is not a camera with arms and lower body parts like a 1st-person-shooter videogame.
In most cases you don't describe the MC in any detail because the reader is not meant to 'see' the MC as if in a movie, rather they are meant to experience the world through the protagonist's experience, sharing their feelings and perceptions. The more specific the MC is in the story, the less universal they become.
When we look in the mirror we tend to see our flaws, not objective reality. I suppose some personality types do not see any flaws in their reflection – and both could be considered unreliable. Remember an unreliable narrator is a plot twist, they come-on as universal and relatable before pushing the reader uncomfortably away from that self-identification. But most people can't be objective about themselves. There will be some bias, some revelation of character, and perhaps most important, the reader sees some of their habitual routine and how they treat themselves.
Avoiding their reflection indicates they don't enjoy their own appearance but value aesthetics –– that's a conflict. A beauty who spends lots of time in front of the mirror is vain, until it flips and becomes insecurity –– again, conflict. Anything that tells us something about their interior – something they wouldn't acknowledge themselves – is infinitely more interesting than straight (factual) descriptions.
But we don't look in the mirror and count teeth, or remark on our long blonde hair and perky breasts, or how much we've come to look like that one dead parent, or recount a laundry list of ethnically-defining skull traits and pigmentation. We definitely do not see ourselves as children, or have info-dump flashbacks about that forehead scar we see everyday.
Factual descriptions not at all necessary to understand a character. At worst these are distractions that kick the reader out of their empathic identification, which is probably necessary for the story to work.
If you want objective descriptions use an omniscient 3rd-person narrator instead.
