The best is 1, which is perfection. The costs are right as projected. The worst are <1 -- this is an over budget project.
Those that are >1 may be good or bad. If you are too far behind in budget (say more than 10-20%, chances are the estimates you are working with were unreliable and you have possibly locked in funds that could have been productively spent on other projects. You should re-estimate the project to see if funds or resources can be released for other work.