Can you please explain bankroll for the non technical user.
I have old coins in my wallet, why i need bankroll, why it is not done automatically ?
How can I explain this to my granny who want to use BBP? she doesn't knows anything about computers, she just want to buy some BBP and leave the wallet open few times a day and receive some rewards for POG.
exec bankroll - its like getting change from a cashier, but you set your own quantity and denominations.
For example, let's say you have 500k BBP, you want to make into qty 50 x 10k BBP.
You would type:
exec bankroll 50 10000
You should have many identical outputs. 
You must specify type: IE 'exec bankroll quantity denomination'. IE exec bankroll 10 100 (creates ten 100 BBP bills). (code -1)
More details here: https://discontinuo.us/biblepay-unofficial-wiki/proof-of-giving/how-to-setup-biblepay-proof-of-giving-pog-using-new-wallet
Thank you. It is clear what bankroll does. Now the question is: Why should I do that? What is the benefit?
Q: Do I need to use exec bankroll?
When you tithe in Proof of Giving, you may tithe 10 BBP, but the max coin value could be as high as 25k BBP (version 1.1.8.7). So, you split your bankroll into denominations so you can maximize your tithing.
Q: Why would I split into 25k denominations instead of 5k?
Splitting into 25k BBP would allow you to tithe almost 100% of the time.
Let's say the difficulty only requires a denomination of 3k. Either 5k or 25k BBP denomination qualify for tithing. A denomination of 5k means you can tithe 5 times, while a denomination of 25k BBP means you can only tithe once with the same 25k BBP.