But it is necessary. Either you want the line to be evaluated or you don't, if you don't, you should use the n switch, and it's extremely rare that a script will result in a need to evaluate the line from a $read call, it almost never happen in practice, and it's very dangerous to evaluate unknown content, via a different exploit someone may be able to write code to that file.
The t switch is also almost always required in practice because the content of the file is either unknown, or it's known but the first line is not representing the total number of line. So in practice, not using the t switch will only result in some $read failure when the first line is a number, rather than doing any good to the read call by not using it.
Not using the t switch will only result in failure but not using the n switch can result in someone evaluating code behind your back etc.
You used "wt" switches for the first $read call and then you didn't use the t switch to get the whole line, your t switch usage is not consistent anyway.
And as pointed out evaluating will only make it slower.
Always use the n switch unless you specifically want to evaluate the line, and always use the t switch unless you control the first line of the file and it's a number representing the total number of lines in the file.