Marco Russo and Alberto Ferrari dig into the nuance:
The goal of visual calculations is to simplify some reports and calculations, rather than to optimize performance. However, it is common sense that – in some scenarios – visual calculations can bring some benefit from the performance point of view.
The main idea is that a report may precompute some values and then, to further elaborate on them, it may use the content of the virtual table rather than recompute the values multiple times.
Read on to learn how you can adjudge what that visual calculation is doing for you in terms of performance relative to alternatives. But hey, if you’re stuck with Power BI Report Server, you don’t have to worry about visual calculations potentially slowing anything down. Mostly because you don’t get visual calculations.