Ok, I admit that I don't have hard facts, but my subjective impression is that pretty much everybody play the nirensei (two 4-4 stones on adjacent corners) almost always when playing as white. There is a reason for this (like komi), or is it just a wrong impression?

i play because of 6.5 komi.
i feel that white has advantage with 6.5 komi and that opening will help me maintain balance best. less complication.

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"The more we think we know about
The greater the unknown"
Words by neil peart, music by geddy lee and alex lifeson

It's a very flexible opening, if you're not sure how to respond to something, ni-rensei is usually a good default.

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Tactics yes, Tact no...

If you finish both your corners in one move with a 4-4, then you can set about wrecking whatever cool framework black builds without always thinking "Hey, I need to make a shimari with my 3-4".

(Shhhhhh, don't mention that making early shimari from 4-4 is popular these days).

Is it? With what purpose?

In general, because of the modern focus on territory. Also it is a thick move and prevents an approach there, so for example it is popular against the Chinese opening to reduce black's potential on the lower side:

Click Here To Show Diagram Code

[go]$$c Early 4-4 shimari
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 2 . . . . . , . . . . . 1 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . 5 . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 4 . . . . . , . . . . . , . . . |
$$ | . . . . . 6 . . . . . . . . . 3 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Most people who play it think it's the easiest, most straightforward opening.

However

...it's not really the case.

Is anything straightforward in go?

But the 4-4 is usually the first opening move you learn about, when someone starts telling you about corner-side-center. There are a number of ways to settle your corner peacefully. It's flexible in its use and it at least doesn't call for immediate complications. For all these reasons, most people are fond of nirensei early on. And I think it makes sense at low level to experiment with it before you set off to try other things.

Exactly. This is why I do it.

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a1h1 [1d]: You just need to curse the gods and defend.
Good Go = Shape.
Associação Portuguesa de Go

As I got it, the nirensei is good for white because it is a flexible opening to deal with any black plan (white starts in gote), and you can afford to avoid complications because of komi.

It makes sense, thank you all!