What is most important to determine when understanding missing data?

What are the advantages and disadvantages of common missing data methods?

When might one use as a threshold or guideline in terms of when missing data be estimated vs. deleted?

referance

Kang, H. (2013). The prevention and handling of the missing data.Korean Journal of Anesthesiology,64(5), 402-406.https://doi.org/10.4097/kjae.2013.64.5.402

Peng,C.Y.J., Harwell, M.,Liou,S.M.,Ehman,L.H. (2006). Advances in missing data methods and implications for educational research. InS.Sawilowsky(Ed).Real data analysis.Charlotte, NC:Information Age Pub,31-78.