Tables are designed to display numerical data. If the cells of a table contain multiline text and images it looks like a questionable way. In this case, it is better to avoid presenting the data in a table.
Too thick lines in tables create noise and block attention. When reading a table, it's better to see the data itself, not the borders. So thinner and lighter lines are more comfortable to read the table.
Often lines and borders are not needed at all. This only increases the readability of the table. Sufficient spacing between table rows is quite good as separators.