Expanding a bit on Charlie83's comments from my experience:
On some Airbus A320 family aircraft there is an issue with the Autothrust function if you use speedbrake when flap is deployed (usually an issue with Flap 2 and greater) whereby the Autothrust settles the speed at about VAPP + 10kts and makes no effort to reduce it back towards VAPP once fully configured.
As Charlie83 quite rightly states - turning the autothrust off (engages thrust lock momentarily) and then back on again rectifies this issue.
Other example - We used to have a rule in a previous company that we couldn't land the A321 with Autothrust disconnected (tailstrike worries). So pilots wanting to practice manual thrust approaches would press the autothrust button, then reselect the thrust levers to the CLB detent to re-engage the autothrust.
If the workload suddenly gets higher than expected on a fully manual approach this is a great way to reduce the workload again... I always brief how I will re-engage the automatics if I am going to fly fully manually...
Cheers
PS