Speed up/slow down
In general terms, and I'll keep it simple, think of the final approach sequence as a chain. Everyone in the chain needs to do the same speed, so they dont run up each others arse, etc. If you are not yet in the 'chain', then you may be sped up, slowed down, held, whatever until you enter the 'chain'. eg. your gap in the chain is a space that is a 15nm gap between 2 others in the 'chain'. Your current position, however, is 1 nm in front of the guy who will be behind you. Now, the controller could just let you run at your desired speed, say 280kts, and it will work fine with the one in front of you, but the one behind you, and every other subsequent a/c (could be 50) will get slowed down/extra miles. Or, YOU could get told to do max speed til you fit perfectly into the hole, then told to reduce to 250kts (the speed of everyone in the chain), to assume your position in the chain. The less time and space the controller has to work with, the more dramatic the speeds/vectors need to be.
There are ever more complex variations of this, but thats the guts of it. The longer the chain, the more of this you expect. Back when the 'chain' at any particular oz airport was short ie 3 a/c at any given time, then there was hardly any of this that was noticeable to the pilot. Those days have gone, especially during unplanned events such as wheels ups/wx etc etc.