ETOPS
the fuel crossfeed check is done on 737 and I am assuming all twin engine jets as part of a set of procedures to allow a comapany to operate greater than 1 hour single engine flight ( approximately 400 nm 737) up to 2 hours 737-400 and 3 hours 737-800 from a suitable airport for landing. If you lose 1 engine you will need to access the fuel from the other tank and checking the crossfeed valve functions will be a pre requisite to allow the next sector to be operated extended range. The tech log entry records that the check has been made