If you're on the road to process improvement, there will come a time when your initial analysis and base line measurements will indicate where you need to start. You may have a single rogue process that's producing too much variation or one that's piling up the defects or you may have a group of them that seem to be wasting your time and money. If you're lucky, you may hit the jackpot and have all three and in any combination.
This is the fork in the road, where you need to understand the type of problem, not the cause - that’s to be discovered, so that you can go down the correct road with the right set of tools. The born in Hollywood expression of "don't take a knife to a gunfight" applies in that you wouldn't use the same tools for a single rogue process as you would to minimise waste in a production line.
For the former, you would probably be using Control Charts, Histograms and Pareto Charts and for the latter, a Value Stream Map (VSM), a notebook and a stop watch would be more useful. If you have the right tools, you might just come out alive to fight another day.