In your opinion what's the importance of cost and schedule?

To avoid behind scheduling, over budgeting, omissions, errors, rework, queuing, activities being merged, failure to understand the complexity of the project and underestimating cost and schedule.

Effective project scheduling plays a crucial role in ensuring project success.Among other things, the schedule tells the project manager how long it will take to complete the project (or any part of it.) It’s also the basis for preparing cost and resource plans.

If the work performed is as per the schedule the control over the cost is maximum.

agreed with mr. krishna ...........

Project Controls  Minimize Cost and Schedule Overruns

I agree with all experts. Well explained.

Cost and schedule two factors which  tied together during project executing duration 

schedule is dividing a project into several tasks each of them has beginning and finish date as well as cost , some tasks can be changed with more cost, like hiring more workforce, or paying extra to expedite materials You want to find the ones that are without cost, finding out exactly why each task on your critical path is in that path. You can also question the duration of each task, some people like to build in extra schedule time for their tasks to take care of the unexpected (like being asked to do it quicker!). If you can discover this, you can shorten the task durations, as well. These are not new techniques, this is just knowledge work. 

As advanced Cost and schedule have a key factor in the project life.

Scheduling and cost control are closely-related concepts that serve as the foundation of project management.

Sir - Schedule and cost is close associates of a job, when we are evaluating it. Both increases together. Schedule shows tenure of a project and cost shows the value involved or associated with the project for the same schedule. If the schedule goes wrong and lengthy, cost will be increased and would not be controlled rationally.  To make a project profitable, which is bread and butter of all, schedule has to be made very efficiently so that project can be finished in time with best level of optimized cost incurred.