As this Register editorial notes (I hadn't known this before I researched it), the practice of setting a limit on the national debt began in World War I, when the government took on serious debt with war bonds. I'm sure that if they thought they could do it without consequence the present Congress would prefer to do away with the debt limit altogether. It always gets raised enough to accommodate the latest borrowing binge, but it serves as a reminder of just how profligate the government is being. It was raised seven times during Bush's 8 years, and again when they passed the "stimulus" in January. But Obama's (and Congress's) spending binge requires that it be done again, and this time it's the Democrats who want to make sure it's done as far away from the November election as possible. So they're attaching it to a defense appropriations bill in the hope of spinning any opposition as reluctance to "support the troops," that sacred mantra in America's degraded political discourse.
Anyway, it will soon be around $14 trillion. Hope your grandchildren aren't planning to grow up to be slackers. They're on the hook for their forebears' profligacy.