+0
Could you please tell me what is the difference between these two sentences? And when should I use each of them.

The roads has been blocked by police.
The roads has been blocked off by police.
+1
The roads have been blocked by police.
The roads have been blocked off by police.

Here, 'off' merely emphasizes completeness.
Comments  
Teachers: We supply a list of EFL job vacancies
Thanks. Emotion: smile
Is it part of duty of phrasal verbs to illustrate the situation? To picture the situation and events.
Yes, often—good observation!