I had heard it relieves strain on the "urinary tract" , especially the prostrate.
When at work/ i am in a hurry though.
At home i do always.

Everyone should pee in whatever position they prefer. Everyone should also clean up after themselves regardless of whether they're drunk, sober or even just old.

Unfortunately many do not do what they should.

In the middle of the previous century I remember going to the courthouse with my Dad, and the urinals there went all the way down to the floor, and slightly below, having been sunk into the concrete at construction. So it was a lot like peeing outdoors, with little concern for aim, or subsequent sitters. I have often wondered why urinals are never installed in private homes.

As a side note, I also remember the spittoons in the hallways. Yes, I’m that old. There was always about a six foot radius around each spittoon of brown slime because chewers would only vaguely aim their tobacco juice as they walked briskly by.

At home all we had was a wooden outhouse about twenty yards from the back door. It was a two-seater. Complete with wasp nests under the seat board. The men never went there to pee. That was what the great outdoors was for. It wasn’t uncommon for women to take similar advantage of the outdoor convenience, although it involved a different posture.

Ah, the good old days!

Eschew “should”; it smacks of authoritarianism.

For more, see the book German Men Sit Down to Pee by Niklas Frank and James Cave.

For various reasons some will and some won't. It's a personal choice.

Nope. Incomplete emptying if sitting.

It depends, if at a park where there's stainless steel toilets how can anyone blame a man for not making physical contact with the toilet seat?
When at home and the guy is drunk or mostly asleep or any other situation where his aim is off sitting down is the most certain means of accuracy available.
Like every other thing in this universe the best answer is relative and dependent on circumstances.
There's simply no hard rule that applies in all situations.

In the words of George H. W. Bush, or was it Dana Carvey, "Not gonna do it".