Yellowing leaves....
 

To cut or not to cut? That is the question

Or rather, when a leaf starts to yellow and die is it best to:

a) cut it off straight away
b) wait until it's totally dead

I'm not fussed about aesthetics so leaving them on isn't an issue. What's the best for the plant?

Leave it till it comes away with a gentle tug. Most leaves have an abcission line where they drop off. Don't cut unless there is some disgusting fungus racing down the leaf.

While I'm at it, what about flower stems?

Wait until the flowers drop or wait until the stem collapses?

Again, it is a matter of choice. Some let them go brown.

Mine are outside on a frame, and when I bring them in for the winter, there will still be some green stems with no flowers. I cut them as low as possible just above a node, then I dust the cut with a fungicide powder. (Mancozeb)
That dries it and acts against fungus.

It depends on the genus. Some of them, like phals, can bloom or grow keikis from old stems. If that's the case I'll wait until is dead and dry.
If not...