I nealy got left behind in. I was day dreaming in the crew room and realised I had about 20 minutes to departure and forgot to 'check-in.' Gate agent kept clearing standby's on while I stood there at the gate. They eventually gave me a seat at the back in a middle seat. Luckily the FA recognised my name on the crew list and had a BFS open.

Theres no requirement to check in but it makes things a lot easier. Same as the report time bot call while being on reserve.