If you're using an older computer (or a tablet), having vibrant Live Tiles may drain processing capability that could be put to better use elsewhere (not to mention battery life with a slate).
However, Microsoft has taken this into consideration, and Live Tiles, which can be found on the Start menu, can be turned off. To turn off a single tile, right-click it and select More > Turn Live Tile off from the menu.
Alternatively, open the Start menu and type the following, then hit enter to turn off all Live Tiles:
Go to Local Computer Policy > User Configuration > Administrative Templates > Start Menu and Taskbar > Notifications in the Start Menu and Taskbar section. Double-click the right-hand 'Turn off tile notifications' entry and and choose enabled in the pop-up window.