One of the greatest motivating forces for Donald Knuth when he began developing the original TeX system was to create something that allowed simple construction of mathematical formulae, while looking professional when printed. The fact that he succeeded was most probably why TeX and later on, LaTeX became so popular within the scientific community.
commands Math latex
This is because LaTeX typesets maths notation differently from normal text. In this instance, you want the sign to appear close to the appropriate element to show their association. Manual sizing can also be useful when an equation is too large, trails off the end of the page, and must be separated into two lines using an align command.
How to use braces in multi line equations is described in the Advanced Mathematics chapter. The AMS American Mathematical Society mathematics package is a powerful package that creates a higher layer of abstraction over mathematical LaTeX language; if you use it it will make your life easier. Just one set around the expression won't be enough.