So never planning to print any work? Ever? What about clients that may want to print your work or portfolio to show colleagues? It's foolhardy not to work in print resolutions and then simply de-res to upload. Just sayin.
What would Caravaggio do?
72 dpi is screen resolution
150-200 dpi is optimal print resolution.
300 should be your base standard working resolution.
600 for high quality work that may be blown up as a poster. Keep in mind that every time you double resolution, you quadruple both the file size and the amount of Ram necessary to handle the file. May need a powerful computer with lots of ram if you plan on complex PSD files that will be 600+ dpi.