I've quite often seen tied notes that could be represented as a single dotted note, like in the example below from a guitar piece. Any help understanding this would be appreciated.
The choice seems arbitrary. Why isn’t the last up stemmed note similarly represented by two tied notes?
To make it easier to read rhythms, especially syncopated rhythms, 4/4 bars are commonly divided into two halves with an invisible barline. This forces visible notes to be seen on the "strong" third beat, even if the start of beat 3 is crossed by a long note. Imagine there being a line here:
There are different opinions, and it's not a hard rule, but it's quite commonly done in pop music, as you've noticed. For whole-notes, splitting is not done, except if someone wants to demonstrate how notation works or something.
Other questions discussing this:
There's a hierarchy. Show the barline (that one hasn't many exceptions, except perhaps when there's a tuplet across a barline). Show the mid-point of the bar. Show the beats. But allow simple syncopations.
In this case the music shows the mid-point of the bar, then allows a syncopated notation across beats 3 and 4. When I first studied elementary music theory in the 1950s this syncopation might have been considered incorrect, and I'd have advised a student taking Grade 1 theory examination to play safe and write a tied note. Now, that would be generally considered unnecessarily fussy.
The basics is to show where the middle of the bar actually is. By making the note a dotted one, it sort of obscures that fact. By tying it across the centre of the bar, it theoretically shows where that centre is.
More and more, however, that idea is ignored, and in 4/4 in particular, notes are written which bridge that margin. Personally, I prefer to see the ties, and immediately know that something is syncopated, but others may have got used to the new idea, and aren't fazed or even bothered.
