Schedule Compression

There are two ways to compress the schedule
1.Crashing
2.Fast tracking

What is Crashing:
It means adding more resources to a project to shorten its duration.

"Crashing" the schedule means to throw additional resources to the critical path without necessarily getting the highest level of efficiency.

For instance, let’s say one person was working on a ten-day activity on the critical path. If you were really desperate to shorten this timeframe, you might add a second resource to this activity. In fact, the resource may not have all the right skills and he might work five days just to reduce the overall time by two days.

On the surface, the prior tradeoff might not make sense. After all, why would you have a person work five days just to reduce an activity by two days? It's not efficient. However, can you imagine a project that was so important that you were willing to make this kind of tradeoff? Think about the YR2K projects. When the end of 1999 was rolling around, many companies were throwing resources onto projects; desperate to get them completed on time. They were fast-tracking.

Reference 1

What is Fast tracking:

Fast tracking means that you look at activities that are normally done in sequence and assign them instead partially in parallel.

Fast-tracking always involves risk that could lead to increased cost and some rework later. For instance, in the example of designing and constructing an application, it’s possible that the design might change before it is finalized, and those final changes may result in having to redo some of the construct work already underway.

A good rule of thumb is that sequential activities can sometimes be fast-tracked by up to 33%. In other words(換句話說), if you're fast-tracking, you can start the second of two sequential activities when the first activity is 66% complete. There is risk involved. However, this seems to be a level of fast-tracking risk that is normally acceptable.

Reference 1