From Faerun Wiki (will probably take most of these):
- Divine powers (demigods) and higher can have porfolio. Two deities of the same pantheon can have the same portfolio, as long as one is a demigod.
- Gods have areas of influence (eg: continent). Outside that area of influence other gods can have the same portfolio.
- Portfolios only changed on death, resurrection or huge events.
- Can pretend to be another god, with worshippers, and try and get their portfolio by subsuming.
- Deities senses events related to their portfolio.
- Greater deity: senses all small events
- Lesser or weaker deity: needs many mortals involved
- Don't need an avatar to get directly involved.
- Can attempt to block other gods sensing?
- Easier to influence world related to the portfolio.