I see this option on all posts, but I don’t know when or how this is to be used.
Thank you.
I took it as, like when you balance your checkbook and you put a check mark in the reconciles box when the transaction clears your account. So one a deposit actually posts to our bank account and is no longer pending I mark it reconciled in TroopTrack
The above from @troop40072 is correct. 
However, not everyone chooses to use it, so it may be a superfluous feature for many troops who elect not to use it.