The total scope of work matters. Are we retrofitting and entire bath or moving a toilet? These are the questions to ask. I take out as much pipe as makes sense. Things that factor into that are age/condition of plumbing and code requirements. We never take more pipe then the customer is comfortable with price-wise, while at the same time encouraging replacement of as much bad pipe as possible. It’s always important to remind the customer that you’re not there to spend their money. Your just there to solve their problem.
This kind of problem is super common in metropolitan areas like New York City and San Francisco. First, you really need to carefully evaluate the system to identify compliance issues you'll run into during repairs, maintenance, and upgrades. These often include outdated materials like galvanized steel or cast iron. After identifying what needs to be replaced, I typically opt for modern materials like PEX or copper because they're durable and easier to install, especially with archaic plumbing systems in older buildings.