Nucleic acid purity also provides a decision point to proceed with downstream assays or not based on 260/230 nm or 260/280 nm ratios.
Once the nucleic acid is purified, most downstream assays require quantification of DNA or RNA before you begin. Nucleic acid quantification methods include measurement of fluorescent DNA or RNA binding dyes, measurement of absorbance at 260nm wavelength, and qPCR.  Nucleic acid purity also provides a decision point to proceed with downstream assays or not based on 260/230 nm or 260/280 nm ratios.