Yes.  During the year end close process the historical tables in the database are updated.  This means that donation totals and attendance totals are all moved to the "previous year" buckets.

If you do not close your year, you will not be able to close your current year batches.

The year end close is a pretty painless process.   When you start Roll Call up in the new year, you'll be prompted to do the year end close.  Make sure all your batches for last year are closed before you answer yes to this question.  It is also a very good idea to make a copy of your data file before you do the year end close.

1)  The first prompt will ask if your system's date and time is correct, if so, answer Yes
2)  Next click the CLOSE OUT NOW button
3)  Click No Thanks, if you've already backed up your data file
4)  Next you'll be prompted for your envelope numbers.  If you'd like to keep the same envelope numbers as last year, answer YES.  If you've entered new envelope numbers for "next year" and want to use those numbers, answer NO.
5)  The last message you will get is "Data Integrity Check Complete".  Once you get this message your year end close is complete.