For a new product launch a business needs to answer both 'how many customers will buy?' and 'why (or why not)?', so the usefulness of quantitative and qualitative research depends on which question matters most at each stage.
QUANTITATIVE research (e.g. a large closed-question survey, secondary sales statistics) is useful for SIZING demand: it produces numerical data — percentages, average willingness to pay, forecast sales — that can be summarised with statistics such as the mean and mode and compared over time or against competitors. This helps the firm decide price and production volume and supports objective, evidence-based forecasting. Its weakness is that numbers do not explain the REASONS behind them: a survey may show 40% would buy but not why the other 60% would not, and poorly worded or leading questions can distort the figures.
QUALITATIVE research (e.g. focus groups, in-depth interviews) is useful for UNDERSTANDING motives: it reveals attitudes, emotions and objections, which is invaluable when refining a new product's design, branding or messaging. Its weaknesses are that it is subjective, harder to generalise, and usually drawn from small samples, so it cannot reliably estimate market size and can be influenced by a dominant voice in a group.
The strongest approach is therefore not to choose one but to COMBINE them, using each for what it does best — a common technique is to run qualitative research first to shape the product and generate hypotheses, then quantitative research to test demand at scale. The most appropriate balance depends on the firm's OBJECTIVE, BUDGET and TIME: a cash-rich firm launching a major product can afford both, whereas a small firm may prioritise cheap qualitative insight plus limited quantitative testing. The justified conclusion is that quantitative and qualitative research are COMPLEMENTARY: relying on either alone leaves a blind spot, so combining them gives the most reliable basis for a launch decision, provided the firm remains alert to sample bias in each.