Sugar and egg whites do well with a little copper in the mix....tomato sauce does not.
It's a matter of what the pan will be used for.
Linda C

The reason for lining them is reaction t acidic foods. Copper like cast iron is highly reactive, and if you cook acidic foods or liquids in them will leave a nasty taste to your food and cause extreme color changes to the food and pan.

I am no expert but my understanding a copper linned pan or ketle is ideal for candy making assuming it is not acidic. Jams could be problematic with the acidic issues.

Old time jelly kettles and apple butter kettles were traditionally copper...
I have eaten apple butter out of an unlined copper kettle...tasted fine, and didn't seem to hurt me....and wow! Was that kettle ever clean on the inside!! That apple butter removed every trace of tarnish!
Linda C

"That apple butter removed every trace of tarnish!"

That would mean that all the tarnish ended up in the apple butter. :-(