It depends on other factors. A very thin trace is OK, if that trace does not need to carry much current. How much current it needs to carry is a function of the larger design, and cannot be determined from a picture of the layout. Another factor is frequency range. If high-frequency signals are next to each other in long runs, there can be capacitive or inductive coupling between them. Again, it depends on the larger design. If a trace is only carrying 20 ma. to an indicator LED, then it need not be routed very directly, or with a large trace. But if a trace carries a very high frequency clock, or a high-impedance analog signal, special layout precautions are needed.