Next-generation sequencing (NGS) technologies have revolutionized the field of genomics and provided unprecedented opportunities for high-throughput analysis at the levels of genomics, transcriptomics and epigenetics. However, the cost of NGS is still prohibitive for many laboratories. It is imperative to address the trade-off between the sequencing depth and cost. In this review, we will discuss the effects of sequencing depth on the detection of genes, quantification of gene expression and discovering of gene structural variants. This will provide readers information on choosing appropriate sequencing depth that best meet the needs of their particular project.