When properly done, the Mandelbrot-type fractals are a map to the associated Julia-type fractals. Using Switch mode takes advantage of that to find interesting Julia locations more easily: if you turn on Switch mode and mouse around the boundary of a Mandelbrot fractal, you are likely to find nicer Julia settings compared to Select mode, which includes lots of boring settings. But both modes have their uses; use whichever you prefer. Note that Switch mode works from Julia to Mandelbrot as well, but that is not very useful; I rarely go that direction.
When properly done, the Mandelbrot-type fractals are a map to the associated Julia-type fractals. Using Switch mode takes advantage of that to find interesting Julia locations more easily: if you turn on Switch mode and mouse around the boundary of a Mandelbrot fractal, you are likely to find nicer Julia settings compared to Select mode, which includes lots of boring settings. But both modes have their uses; use whichever you prefer. Note that Switch mode works from Julia to Mandelbrot as well, but that is not very useful; I rarely go that direction.