These vials are mainly intended for analytical chemistry / sample preparation applications, such as:
Autosampler vials for Liquid Chromatography–Mass Spectrometry (LC-MS), High Performance Liquid Chromatography (HPLC) or Gas Chromatography–Mass Spectrometry (GC-MS) instrumentation. For instance one vendor says: “Our 2 mL clear glass screw‐top autosampler vials … are the perfect fit for HPLC and GC instrument platforms across a wide variety of applications … proteomics, metabolomics.”
Storage of small volume samples/aliquots, especially when you want to label/identify each sample easily (hence the write-on patch).
Sample preparation: dilutions, derivatisations, or transferring of small volumes prior to injection or measurement.
When low volume, high sensitivity, contaminant-free sample handling is required (for example, “LCMS certified” vials: minimum contamination, minimal effect on pH, etc).