Question -Substiution ALWAYS imagining invisible brackets in your head?

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Im in 2nd year of math now...so I know algebra but

I was reading this from this website:

"Substitution
Every time we replace a part of an expression with a value or another expression, we are using the technique of Substitution. And, every time a substitution is performed, parentheses are used!"
http://www.math.ohio-state.edu/~mcginnis/08Au%20M132N/Algebra%20Fundamentals.pdf

My question is...
when you substitute into an expression...eg.

e^x Sub in 2x+1 ...

Maybe a bad eg since I am typing it ...but if you were writing it on paper...

I wouldn't even think about it...id just write e^(2x+1) ...(No Brackets)

Or sub 2x for x in x+1 ...Id just write 2x+1


or sqrt(x^2+y^2) ...evaulated at x=1=y Id just go sqrt(1^2+1^2)


But do you ALWAYS imagine brackets in your head first...when youre doing these...

Because I am really worried that everyone else is doing this except me ..
 
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I wouldn't write things the way you are writing. I would say "substitute x=2y+1 into exp(x)" otherwise you're bound to get confused.

I think I would only "imagine brackets" when necessary. So, if all you're doing is adding things then it doesn't matter, but if you were to evaluate, say, "substitute x=1-y into 1-x" then ignoring the brackets will get you into trouble.