In this metaphor, all code (new or old) is a liability and the revenue/value stream derived from it is the asset. As a developer, you're trying to maximize assets minus liabilities. It's okay to take on a liability as long as it's balanced by a greater asset.

But buying on margin increases your volatility and risk exposure, so you shouldn't take on more than you need to. Assuming zero transaction costs, it's always a good idea to substitute less code for the same benefit.