But not all slippages mean a loss. Positive slippage can occur if the price goes down while you place a buy order or increases if you place a sell order. Although it is uncommon, positive slippage may occur in some highly volatile markets.
Wrong. There is nothing like positive slippage. There is no way the price goes down after you place your buy order (or up after you place sell order). Its not caused by your order. You just created limit order and price went up and filled your order. Its not positive slippage. Its limit order that was filled.
It occurs in markets with high volatility or low liquidity.
It occurs almost always. The only moment you was not affected by slippage is when your Oder is filled with first bid/ask or you put limit order under present spot price. The size of slippage depends on market liquidity (which can be low/high regardless of volatility) and your order size.