Hate to admit it, but I haven't closed my company's modules since 2010. The new BF modules are a lot more lenient for allowing modules to remain open (better table structure for dates). I would suggest keeping on top of things from a client perspective so that data is purged according to the retention policies established in the set up tables.
Any legacy modules should be kept current due to the current period, one future period restrictions.
And of course, you should close the modules to prevent incorrect dates from being entered.