Seventh chords

I understand relative majors and minors butwhen do you throw in 6ths, 9ths, 7ths etc...

Like All My Lovin by the beatles the chorus is Bm, F#7, D

But seemingly you could just use F# and the melody would still fly... Why do people choose then seventh chords when it really isn't necessary?

Is the or rule to this or is it just something you feel out with your ears?

yeah they just spice up the progression a little

no office about what do you call "all my loving"?????? that isn't the verse never mind the chorus. and the B7 is very important to the song.

Dominant chords are part off the perfect cadence(V7 I), is how in music theory he get many ideas on how thing work.

there are many theories on extended harmony i can in no way go throw them all nor the one i do know here. they are very much necessary.

Now own that point can they be put in to mix things up a bit of course, help the melody along or course, crated a chord/melody to the song of course, with out changing the basic structure of the song of course but they are very nessary

Whaaa....? !

Take a chord out of a Beatles tune!? (or change it) that'd be sacrilegious.

chords are paints: mix them this way get bright-red, mix another way and get dark-red, etc.
...as with everything "the devil's in the details"

example:
Beatles - 'Hard Days Night'

Ya know that famous first chord, played on a Rick-12-string Elec and strummed down (hard) ONCE at the very begging? Its a G4
it hits
G4 & Riiiiinnnnggg!
"its been a....
then to G major for the rest of the tune (V= G D G F, if memory serves)
a few minutes later, just as the tune fades quickly you hear the G4 one more time , being picked lightly ... fading.

were it not for those brilliant song-crafting choices 'Hard Days Night' might never have become the quintessential piece of Pop it is.

(more than once) I've had a student ask if he could learn a Beatles tune ... i play that G4 and he smiles and opens eyes wide.. "is that Hard Days Night?" -- "yes"
How did he know?
Because of that unmistakable G4, thats how.

When you have been playing a bit longer your ear will "tune" itself to these tonal changes much much more easily and you will 'feel' the "why" of a chord (even if ya don't like it, lol).

RAWK!
Cs

Hahahah! Hilarious! That would probably be MY reaction, too. I mean, just reading about it got me smiling with eyes wide open. LOL!