Subordinate Conjunctions and Relative Pronouns

*OBEJCTS ARE THE SAME IN BOTH SENTENCES

You have a problem.  You get stuck on it. 
You have a problem that you get stuck on.
You have a problem you get stuck on. 

I have another friend.  I have never worked with her. 
I have another friend whom I have never  worked with.
I have another friend I never worked with.
 

It is something.  I know how to do it.
It is something that I know how to do.
It is something I know how to do. 

It is an important thing.  We have to take advantage of this. 
It is an important thing that we have to take advantage of. 

It is an important thing we have to take advantage of.

I finally signed the document. 
I should have signed it yesterday.  

I finally signed the document that I should have signed yesterday. 

Tarifa is a place.  You can go there to relax. 
Tarifa is a place where you can go to relax.  

*OBJECTS ARE DIFFERENT.   Second subject refers to the entirety of the first sentence.

The the project´s due date has been extended. 
This is good because otherwise we would not have finished on time. 

The the project´s due date has been extended, which is good because otherwise we would not have finished on time. 

The weather will be nice this weekend. 
This means we wont have to cancel our plans. 

The weather will be nice this weekend, which means we wont have to cancel our plans.