Articles are like adjectives and they are used to modify Nouns.
However they are divided into two types:
Definite and Indefinite
the = definite article
a/an = indefinite article
The is used to refer to precise or picky nouns; a/an is used to adjust non-specific or non-particular nouns..
You can't just consider them fillers, and take them off a certain expression because you believe it's useless:
I read the book
is not like
I read book
I am saying this, because I have received and read comments, that's exactly asking the writer to remove such articles in such situations.
If the book is a specific one, then we say : I read the book, if it's any book then we use : a
I read "a"book"
Hence you replace the article, you don't just get rid of it.
"A" and "an" means that the noun that's modified is indefinite, referring to any member of a group. For example:
E.g : My sister wants a pet on her birthday. Any pet because we did know decide what pet we are going to buy her, which is indefinite.
Notes on a/an:
1)"a" is used before every singular noun that begins with a consonant : A Cat, a table...
2)"an" is used before every singular noun that begins with a vowel, or a pronounced H.
Except irregulars, or special cases.
3)"A/an" can be used only with count nouns.
Notes on "the":
1)The can be used with noncount nouns, or the article can be omitted entirely.
2)The definite article is used before singular and plural nouns when the noun is specific or particular
Do not use the before:
names of cities, towns, or states:
names of streets
names of lakes and bays
names of mountains, continents,
I know that all of use know these, but perhaps it was needed to remember and remind, that they are not only fillers, neither determiners are (this, that, those, these) , nor quantifiers are useless.
We can't always just consider them fillers, and useless, they do have reasons, or obviously modern Grammar wouldn't be still based on these rules. So don't underestimate their usage.