Never use a cruelty when a joke will do in its place

The tilde represents a "nasalized vowel" and is just like any other accented vowel in that it has it's own distinct sound. According to one source I found, "the most distinguishing feature of Portuguese spelling is the use of tildes on vowels (ã), which indicates nasalization in certain diphthongs. This accounts for the fact that some Portuguese words (e.g. São Paulo) sound like they contain the letter n when they really don't. The tilde occurs exclusively in diphthongs (e.g. ãe, ão, õe), and is not always printed, but it's still easy to recognize these diphthongs and infer that the sounds should be nasalized."