Tableau employs good practices for formatting and visualization from the time you start dropping fields on shelves. You'll find that the discrete palettes use colors that are easy to distinguish, the fonts are pleasant, the grid lines are faint where appropriate, and numbers and dates follow the default format settings defined in the metadata.
The default formatting is more than adequate for discovery and analysis. If your focus is analysis, you may not want to spend too much time fine-tuning the formatting until you have moved on in the cycle of analytics. However, when you contemplate how you will communicate the data to others, you might consider how adjustments to the formatting can make a major difference in how well the data story is told.
