FR24 is invaluable for this. Had a connection at LAX with AS recently

Using the onboard wifi, I could see the assigned aircraft was way behind schedule on earlier flights, so was looking like a big delay, so started looking at alternatives.

When the notification came through, e-mailed the BA Holidays Duty Office straight away, and they moved me onto an earlier connection. Worked out perfect in the end.

If I had waited until I was informed the connection was going to be delayed - it would have been too late.