This approach to adding emphasis or drawing attention to one part of a sentence is rather grandly called ‘existential there’ or ‘transformational there’.
Now, this is astonishingly simple, and how it can be a CEF C2 grading marker, I’ll never know! But look at how it moves the emphasis:
A stranger is standing on the porch.
There’s a stranger standing on the porch.
In the first sentence ‘is standing’ takes the a low-peak emphasis at the beginning of the sentence with ‘on the porch’ being the main focus, whereas ‘a stranger’ is the main focus in the second. So now we’re intrigued by this stranger, and we care fairly little about where he’s standing — though it does add a nice bit of setting description.
What about these?
No tickets were available this morning.
There were no tickets available this morning.
Similarly, emphasis is moved from ‘this morning’ to the main point of the sentence: ‘ no tickets’.
Again, the stress moves from the end of the sentence, to the word we want to emphasise.
All of these approaches help to move the subject away from the front of the sentence and into an emphatic position, into the place that we, as competent speakers of English, put the emphasis.
A Word to the Wise: Sentences beginning with ‘it’ or ‘there’, and using ‘to be’ constructions should be used with care. Make sure that you don’t overuse these patterns – and ONLY use them when they add emphasis appropriately. Like anything: too much is a bad thing.
They can be boorishly heavy-handed approaches when overused, and make your writing repetitive and immature. So, you have been warned. After all, no-one wants to be repetitive and immature, do they?!