OK, that may be a bit harsh. But the danger is that a translation that is out-of-date or badly done will turn you off the book. Many classic books whose translations are now beyond copyright are available for free. But these translations are, generally speaking, poor. To really appreciate these books, find a translation that is up-to-date and that suits your reading style.
When you also have the original text, whenever there is a more interesting or obscure paragraph you can look to see what was really said, possibly with the help of a dictionary.
Even when the translation is good, the translator cannot stop at each sentence and explain why certain English words have been chosen, which may be the closest to what was said, or they may be not, but the translator has thought that the chosen translation is easier to understand for an average reader.
The older translations (and perhaps the future translations, taking into account the current trends) also avoided to translate whatever words were considered offensive when the translation was done.
I pretty much guarantee that unless the translation is completely atrocious, what you will gain from this will be even worst. Languages just don't work like that. Trying to fugure out nuance or meaning from word for word dictionary analysis just don't work.
For some of the ancient texts there are editions with commentaries, which include both the original text and an approximate translation for it and in which most of the less usual words and phrases are discussed in detail, to establish their most probable meaning.
While such a commented edition may be the best tool, what they add over a bilingual edition and a dictionary is much less than the difference between the latter and an English-only edition.
The English translations may be more acceptable for literary fiction (where for many people it matters more to be entertained than to know what the ancient author truly said), but they are particularly bad for any text that has any scientific value, e.g. Aristotle, Plato, Pliny, Herodotus and so on, because the translator normally lacks expertise in sciences and is unable to identify the appropriate English words.
Even in Homer, there are many names of animals, plants and minerals, or even of colors, which are normally mistranslated into English.