When laying out a complex board with lots of densely packed ICs and lots of traces, the trace size is usually picked to allow routing the most traces possible without making fabrication difficult. A typical digital PCB design might use 8 mil trace and 8 mil space rules, for example. This means that the smallest trace width is 8 mils (0.008 inches) and the minimum space between any two traces or circuit elements is 8 mils. Some really dense boards go even smaller. 20 years ago, I typically used 12 mil space and trace rules (with DIP packages and no surface mount). This is small enough to allow running traces between pads of a DIP package.
Exceptions to the standard trace width are usually made for power routing. Here, power and ground traces are made as wide as possible, to minimize trace resistance and voltage drop when high currents are flowing.
In general, it's a good idea to make all traces as wide as possible, after all traces are routed. Practically, though, it takes a lot of time and effort to manually go through a design and edit trace widths and move things around when it's not really necessary.
On small layouts like most stompboxes, wide traces are great. Actually, minimizing the NON-copper area of a board will save you on etchant costs as well.