SQL SERVER QUESTION

I am still new to web programming. I have a question regarding sql databases. Since variables in php don't require a type, why is it so important that you specify a type for each of the colomons in your tables in your sql database. It seems to me that you could potentially make everything chars and it wouldn't make a difference. The only real benefit is that I have seen that by making a column of type date, it allows you to easily compare dates. I don't see the benefit of making a colomon of type money though? Thanks, Dale