Hi Jimmy
In a nutshell, the role of Ops is to try and make what the Planning guys have planned actually happen on the day whilst trying to avoid any excess costs or disruption. A typical charter operation will on paper have a particular aircraft planned to do 3 return trips on a busy day, but if that aircraft has been delayed or taken out of service then Ops have to come up with ideas to get the programme back on track.
There are a multitude of events which can conspire to make sure Ops don't have a quiet day, eg:
Technical problems - if you have a spare at base it'll probably be a quick fix but if the a/c needs to go in the hangar or the only spare is in Kuala Lumpur then it could be grounded for days.
Air Traffic Control delays - some can be avoided but generally with an increased cost due to rerouting or flying at a less-economic flight level.
Crew hours limitations/sickness - if a crew on a long duty get a problem downroute then they go out of hours and the plane is stuck there until they are legal to fly again.
Weather - fog, snow, thunderstorms, etc can all cause delays/diversions.
Passengers - late pax to the a/c may mean having to offload bags causing you to miss your take-off slot and picking up a big delay which could then cause crew hours problems. Drunk/offensive pax can cause flights to be diverted en-route.
Airports - baggage belts break down, a/c get hit by ground equipment, handling agents can be short-staffed, especially if you arrive late.
If an airline has lots of spare aircraft and spare crew and lots of turnaround time between flights then Ops would be an easy job, but they never have so Ops have to make do with what they've got and try to minimise the disruption without spending a fortune on welfare, sub-charters, empty sectors, etc.
I hope that's given you an insight
Cheers
Alan