The border-collapse property is great for making borders even all around <table> cells. It makes for a clean look that I actually prefer.
But, there is something that can cause issues with how a browser draws the cells and their respective borders. Each cell is placed under the previous one when being drawn in order. This means that if tables have different colored borders, those borders are hidden on some sides.
In the code example below, hover over cells to see how borders can be hidden behind each other.