I made this rule for myself.
Each step in my process should improve or at least maintain the purity and quality of my solution. If this is not so, if any step in my process does not maintain or improve the quality of my solution, then it shouldn't be in my process, alternatively if there is a step I should be taking in my process, that does produce the desired results, then I should include it as part of my process.
Different acids act upon different metals, differently. This is why a combination is required to dissolve Au into solution, only one or the other will not do it. Also consider this, a drop or two, at the correct step in your process, of sulfuric acid, will precipitate lead sulfate, removing it and promoting your desired end result.
Reading Hoke is the best possible thing you can do with your time, if you are just starting to learn about all this.
Scott