Why can redirection be combined in an assignment statement?

[Peng Yu]

I can not see why redirection is allowed in an assignment statement.
For example, redirection in the following command does not do anything
useful.

x=10 < /tmp/1.txt

Is there a useful situation in which redirection does do something
useful in an assignment statement? If not, why not prompt an error for
this case?

I can think of this, which basically truncate or create a new file
/tmp/1.txt, and perform the assignment. But I don't see a point to
combine both in a single line. Therefore, I would not consider this is
as a useful situation.

>/tmp/1.txt x=10

-- 
Regards,
Peng