All data tables should use summary tags and contain header rows. Tables should only be used to display data. They should not be used to determine layout.
Summary tags should contain a brief summary of what is contained in the table. Summary tags provide visually impaired users using a screen reader the ability to determine if they would like to proceed through the table or skip it. This provides visually impaired users the same experience and options as users who are not visually impaired.
Tables should always have header rows this also provides more options for visually impaired users as far as understanding what is in the table. This also helps in being more descriptive and having better quality content which will help search engine optimization.