I use FR24 to check on the progress of the inbound and thus possible delays outbound. However, bear in mind that if you are at one of the airline's home bases, or an airport where that airline has multiple flights in and out around the same time, OPS may well be planning an a/c swap which FR24 won't know about far in advance. It's always better to check in on time and stay relatively close to the gate in the event of last minute changes.