As the name of this G/L suggests, this suspense G/L is a "wash-through" account for automatic system transfer processes such as member journal account transfers, auto check transfers etc.
Therefore this G/L should be zeroed out each day as both sides of the transfers offset each other and wash through this G/L.  However there are certain things that can occur (either automatically or manually) that may cause a balance to remain in this G/L and require manual intervention to clear it out.   The most common offages occur due to one of the following:
(1) Auto/Mail Checks need to be printed - These are automatically system generated checks that sit in a queue until a CU employee takes the menu option to print them.  The money has already "swept" or transferred out of the member's account and is sitting in the 870.07 G/L.  When Tool #632 "Print Auto/Mail Checks" is used to print these checks, an automatic offsetting journal entry is generated and should "clear out" the G/L balance at end of day.  
(2) Part of a transfer was not reversed correctly - Although CU*BASE posts both sides of a transfer at the same time (which eliminates the possibility of only posting half or one side of a transfer), the system actually posts two separate transactions.  Therefore, when reversing a transfer, you must reverse BOTH sides/accounts involved in the transaction.  If one side is reversed and the other side is not, the difference will sit in 870.07 until the second side of the correction is made. 
HINT: An easy way to spot these one-sided reversals is to skim the history of 870.07 for a J/E description starting with 'E/C.'  There should be both a debit and a credit for the same amount with the same description - if there is only one 'E/C' entry, you can run the TR system journal analysis report to obtain the account number and look at the transaction history to find the other side of the transfer that needs reversing.  Once you have the necessary information you will need to perform a member account adjustment offsetting 870.07 to clear the difference from the G/L.
(3) Finally, employees may mistakenly offset 870.07 when performing member account adjustments or journal entries.  Look at the G/L history for the day you go out of balance and look for journal entries performed by Employee IDs other than 'TR' and/or J/E descriptions that are out of place (not system-generated ones like "JOURNAL ACCT TRANSFER PROC"). 

If you still cannot locate your offage, feel free to contact a Client Service Representative for assistance.