when consumers make buying decisions substitutes provide them with alternatives substitutes occur when there are at least two products that can be used for the same purpose such as an iphone vs an android phone for a product to be a substitute for another it must share a particular relationship with that good those relationships can be close like one brand of coffee with another or somewhat further apart such as coffee and tea 
giving consumers more choice helps generate competition in the market and lower prices as a result while that may be good for consumers it may have the opposite effect on companies bottom line alternative products can cut into companies profitability as consumers may end up choosing one more over another or see market share diluted 