Join Date: Jul 2005
Location: London, ARN, HEL, ..... or MAN
Programs: BA GGL / GFL, Mucci Diamond!, HH Diamond, Radisson VIP, FB Gold, LH Sen, Hertz Gold
Posts: 6,481
There should be no downside to not checking in before you get to the airport as far as I know.
If you have selected your seats, they should be safe unless you miss conformance. I like to check in online as my booking then sits on my home screen on my phone, reminding me of the departure time of my flight.