Keeping secrets

There are several reasons why a fiction writer might initially deprive readers of information. The most common is that the story is being told in chronological order - the reader knows as much as the characters as they progress through the story. But there are other reasons -

• In a Whodunit the reader's not usually aware of all the past events. There are reasons why some characters keep secrets, and reasons why some other characters (who are representatives of the reader) want to know those secrets.
• There may be a delay giving information to the reader because the Point-of-View character may not consider the matter of any immediate importance. In a first-person piece, it may not pass through the character's mind that they're (say) called Sue, that they're a white woman (rather than a cat), aged 53, living on Earth (rather than Mars) in 1980 and they're childless. Such details often become clear later, indirectly.
  Do such delays matter? Without an initial infodump they're hard to prevent. Sometimes the punchline of a story works by revealing that the reader's assumption about a detail is wrong (e.g. the person's actually in a wheelchair) causing the reader to re-interpret the story (ah, so that's why they never went upstairs).
  First-person pieces in particular are prone to such delays. They can be irritating - rather than guess the gender, age etc (by default giving the persona their own traits), readers may suspend judgement, keeping multiple possibilities laboriously in mind. If readers guess too early and later find out they guessed incorrectly, they can lose their sense of immersion.
• In some books I've recently read there's an info-dribble rather than an info-dump - at the end of chapters a new piece of biographical information is revealed. Sometimes in a first-person narrative the details are increasingly embarrassing, so it's understandable why the info was withheld. More often it comes over as an authorial ploy.
• The withheld information may be in the forefront of the main character's mind - e.g. we're told that they're on the way to a funeral, but we're not told whose; the character tells us that they've just made a huge mistake, but we're not told what.
  It's a standard literary trick to add suspense, but unless it's psychologically justified (perhaps the persona's desperately suppressing the info) it feels contrived to me, an attempt to make musings into a page-turner.
• Information is often withheld because at the time of writing the author considered it irrelevant. However, to the reader the information may be crucial to the understanding of the piece. If, for example, readers don't know the era/setting of a piece, how can they interpret a character's casual use of the "N" word? This contextual information is often provided from outside the text.

A key issue is whether curiosity is incited, or indeed, whether readers even know that information is missing. Some readers want to know about the characters' appearance, the location, etc, and expect to be told the details sooner or later. But not all authors think such details are necessary. Not all first-person protagonists have names.