Dillution of Developer

OK i'm gonna sound ignorant here but I'm gonna ask anyway.

When Developing film (in that tank) what's the differencd with using it straight up, 1+1, 1+3 and so forth?

I know the developing time changes accordingly (following the chart), but what sorta different results to we expect to get?

Less grain? Smoother tones?
Saving more of the developer?

I'm using Kodak D76 and I dilute it 1+1 as i was told.

Do you use it one-shot or re-bottle? How much do
you use each roll? I think those who use it one-shot
dilute 1:1 or 1:2 because it will go that far.

For generations D-76 was only to be used full strength
and with a replenisher. Dan

one shot and dump.
i mix 1:1
just considering use 1:3 to get smoother tones.

Diluting a dev will give you more film speed, and higher grain, but higher sharpness.