There's an up-side and a down-side, of course. Leave 'em turned up and it's possible (or even likely depending on one's age...) that the amp will produce an overpowering 'Screech..!' when the guitar is plugged in. On the other hand, turning it all down implies that there's a pretty good chance (depending on one's age...) that there'll be silence for a while at the beginning of the session, with much testing of leads, looking baffled, scratching of heads etc before the penny drops. It's a no-win conundrum that only you can solve. Personally, I turn it all down, despite the head-scratching risk (yes, I'm old, too...).
Hope this helps.