Speed up in the long term by slowing down in the short term
On most projects there is a tendency for someone involved to become the "expert" in one or more areas. As they become comfortable and more knowledgeable in an area they will naturally gravitate to picking up tasks related to it. The need to deliver as quickly as possible can also drive this as the person who knows most is likely to be the person who can do the work quickest.
Over time this can lead to a situation where knowledge of the project becomes "siloed" (isolated) - each person has their own areas of expertise and there is less and less cross-over and sharing of other areas. This leaves the project massively exposed if a person leaves or is on holiday. It can also add delays as tasks on the critical path may hold up other tasks while the person who can do them is working on something else.
The team I am currently leading took a different approach. They insisted that people pick up tasks in areas they know nothing about. This was difficult to buy into as a leader who has a project to deliver however we have a culture of try things and if they don't work change them. My concern was a natural one that this would mean that the project would be delivered more slowly.
In the beginning of the work it definitely had that effect. Each person was free to choose any task they wanted and were actively encouraged to pick up a completely different task than the ones they had done before.
Progress was slower and there was pressure to deliver faster. However over time this has turned from being a negative into a massive positive. Every member of the team can now pick up any task which means we are no longer as exposed to people leaving or holidays. Productivity has soared as everyone knows the whole project and can help anyone else with what they work on.
People feel bought in and they feel they are contributing. They can engage fully in all the discussions. There are naturally some areas where someone is stronger however one of the key objectives is to pass on that knowledge so others can get up to speed on it.
At the beginning I was definitely sceptical but I am now a complete convert to this approach. It is a difficult sell to the stakeholders however in our case we have been rewarded massively.