When a project is in trouble, usually an outside party is brought in because the problems on the project are bigger than the current project manager realizes or can handle. By definition, troubled projects have major problems. In fact, the problems may be too severe to overcome. There are a number of potential outcomes that could result from trying to rescue a troubled project.
The project is turned around and completes successfully (within tolerances). This is the best case, but it's normally not possible. If you take over a troubled project that is trending 30% over budget, for instance, you are not normally going to be able to turn it around to a point where you finish within budget expectations.
New expectations are set and met. This is a common result of taking over a troubled project. New estimates and expectations are set and then the team strives to meet the new expectations.
New expectations are set and missed. This is also a common outcome if the root causes of the original problems are not identified and resolved. This is actually the worst-case scenario, since the company is no better off after the rescue than they were beforehand. It could mean that the money spent since the original rescue is all wasted.
The project is cancelled. Many troubled projects are just cancelled and the money already spent is written off. One reason for cancellation is that the business return on investment (ROI) projected from the original project may not be there anymore at the higher cost of the rescued project.
The normal tendency for a person arriving on a troubled project is to jump in with both feet to determine causes and create a plan for a turnaround. If the project is small, you may be able to do just that. However, if a project is small, you are not typically going to go through the effort of a project turnaround.