If you store things and somebody asks for them then you haven't got a problem. If you don't store them and somebody asks for them then you might have a problem. I'm a hoarder.
In the days when keeping receipts was required I had 3 tax audits in different years for various reasons. In each case I had to provide receipts for that year. If I had not been able to provide them I would have had to repay the tax rebate I had been granted in that year, i.e. equivalent to losing your tax free allowance in the UK. I still retain all the receipts going back to when the rule was introduced, obviously minus the years I had already submitted. Now it is based on electronic payments made through the banking system but, as an older person, I could opt to use receipts if I wished.
If you read the official police guidance for applying for a biometric residence card, anybody with a permanent residence certificate , i.e. blue, issued more than 5 years before the date of application, is supposed to provide proof that they had not left Greece for more than 5 years since the certificate was issued. One way of doing that would be to submit electric bills showing almost constant electricity consumption during the period. As it happens they don't seem to be enforcing that particular rule but if they had how would you prove it, Mike?
I receive some bills electronically but I also save them to disk. I have every P60 since I started work properly in 1970.
Warwick