As in the title: I am interested in why it is necessary to exclude the constant sequence from the following definition of a functional limit:

Note the $0 < |x-c|$. Why would the definition break down if only $|x-c|<y\delta$ was required?
As in the title: I am interested in why it is necessary to exclude the constant sequence from the following definition of a functional limit:

Note the $0 < |x-c|$. Why would the definition break down if only $|x-c|<y\delta$ was required?
If you allow for the constant sequence, then the existence of the limit implies the continuity of $f$ at $c$ and $L = f(c)$. Using the above definition, you can also handle discontinuous functions.
Edit: As mentioned by Daniel Fischer above, it would be even equivalent to the continuity of $f$.