Lack of disposable income is inevitably a disadvantage in retail, but when customers leave one  market segment in favour of another there is a benefit to those operating in that segment - fast fashion retailers targetting the value market achieve large volume through their low pricing. By providing close copies at a fraction of the cost of the originals they appeal both to low incomes and also higher income groups, who purchase more frequently.

Other disadvantages include sustainability issues - short product lifecycle - more frequent purchases linked with more clothing going to landfill - more transportation - more natural resource usage.
Ethical issues - usage of lowest cost labour risks exploitation.
Reputational risk from infringement of intellectual property rights by making close copies of designs from other fashion houses.