tefilla - How do people daven so quickly, and what's the support for it?

I learned that one must clearly enunciate every word of tefila. At the least this would include Shemoneh Esreh and Shema, but one might presume it includes the entire prayer service. This question can easily apply to whatever definition of tefila one uses.

In many shuls, the prayer leader is generally careful to clearly enunciate every word. However, in some synagogues the pace of prayer is so fast that it seems physically impossible.

Granted, I have been davening for only about eight years, and a lot of these people have been davening for many decades. Still, there's a certain physical limit to rate of speech. It would seem, therefore, that in these synagogues they are not really enunciating every word - that or they are employing some form of kefitzas hadiburim.

I want to stress that I am not in any way condemning this practice or saying that it is in fact better to spend more time on tefila than on learning, which I assume is the impetus to pray quickly in the first place. On the contrary, I think both ways are very good, and I am not passing any judgements at all, Heaven forbid. I'm sure that this practice is well supported.

But please, help me understand:

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  What exactly is the practice here?

  
  
  
  
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    Slurring all words together into a long drone?

    
    
  
  
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    Only saying certain words and scanning the rest?

    
    
  
  
  
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    Only saying the beginnings and endings of each part?

    
    
  
  
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    Something else?

    
    
  
  
  
  


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  Also, what is the halachic support for the practice?