"It was always going to be hard to beat the German team but, as I say, we won." In this case, the speaker is affirming what he's already stated. "As I said before..." "to repeat what I stated previously..." "As I say, if you score goals you win games." "As I say, there is a lot to gain by remaining in the European Union." In these cases, the speaker is affirming something that he normally says. "This is a phrase which I repeat often for its truth ..." "As you say" means something similar. You can use it when someone has said something and you want to repeat it. Occasionally in movies, especially movies set in the past, people will say "as you say," on its own. This means "I am in agreement with you," or "I will comply with what you are asking." Nowadays, the expression "Whatever you say" is more common. A common idiom which includes this expression is "Do as I say, not as I do", which means "act according to my commands, and do not emulate my actions". http://idioms.thefreedictionary.com/Do+as+I+say,+not+as+I+do I hope that helps. Have a good day!

It's supposed to refer back to something said previously. Although it's spoken in the present tense, it really means "as you've heard me say already", or "as you said before" or "I'm concurring with what you said".

It's not really an expression, per se. It's more like a word filler, similar to "umm..." or "uh". That's why you're hearing it in interviews. People are searching for words, try to fill the silence, but avoid saying "umm..." because it can come across as sounding uncertain (or not very smart). So they say the obvious to fill the silence and keep talking before finding their next word, i.e. "as I say..." (Well, yeah, you just said it! :D )

It is used to identify a person quoting/referring to something they have said or whoever they are speaking to has said previously/ in the past. Typically it predicates an idiom. A helpful way to think about it is to add an imaginary 'always' or 'usually' For example 'As I (always) say, "Mind over matter. If you don't mind, it doesn't matter." 'As you (usually) say "Whatever floats your boat."