Why use trim () to trim user-entered data?

I've seen a lot of programs trim user input data with trim,
Why do you do this?

The introduction of the book is to say that it is for the sake of safety.

I'm kind of wondering, which one of the students is talking about

Reply to discussion (solution)

Trim can be???? Space.
If you use?? Into the?? Is
$data = ";
What about using if ($data = = ")? Returns false, because the????
But I?? Look, if it's all in?? It's all spaces, is it intentional,??? Null character?
So use trim ($data); Give me a hand. Space? In addition, if there is a character, then it means to use???, in addition, you can use the space to remove.

Example $data = ' AAA ';
echo Trim ($data); Aaa

It's all right with security, and it's not necessary.

Registration is unavoidable to operate a number of blank space, at least the end of the removal

