A critical realist would see secondary data, as providing partial, but not necessarily accurate, representations from which insights could be drawn.

Secondary data that fail to provide you with the information that you need to answer your research question(s) will result in invalid answers.

Survey secondary data will have been collected through census a distinct subtype of survey strategy.

Primary data is data which can be collected specifically for the purpose of answering a research question(s) and to meet research objectives.

Censuses data are not widely used by other organisations and individual researchers.

Secondary data that succeed to provide you with the information that you need to answer your research question(s) will result in invalid answers.

Velocity of big data is the speed in which data are being constantly added in real time or near real time from a wide variety of (digital) sources.

Ad-hoc survey secondary data will have been collected through census a distinct subtype of survey strategy.

No real control over data quality is one disadvantages of secondary data.

Original purpose of secondary data may not match your need.