any member of a class of words found in many languages that are used before nouns, pronouns, or other substantives to form phrases functioning as modifiers of verbs, nouns, or adjectives, and that typically express a spatial, temporal, or other relationship, as in, on, by, to, since.
As far as I understand, prepositions exist to provide clarity and explicity form relatonships between words. I'm sure you could communicate your meaning quite effectively without them, but it would be a lot easier for everyone if you didn't. :)
In fact, really, there isn't any wrong way to speak. For instance, I have some mentally handicapped friends who speak in a way that many consider incorrect, but if it works, is it wrong? Or is it just different? :)
You might enjoy this article, if you're curious about what I meant.
Personally I love prepositions and think we should use them as often as we could, though. Have a good day!