You could of course use 2♠ as a general transfer and 2NT to ask what it was ment for, but if you bid like that you will get the declarer on the weak hand and the lead will go trew the strong hand, rather then up in the strong hand, there is a reason for why you should transfer and not bid you suite. The reason is to protect your hand, and another point is that the 1NT opener should be only doing what the responder whant him to do. So if you have a transfer bid and a relay to ask what it is, you will find it difficult to investigate more about the 1NT opening hand, since you find that 1NT opener is suddenly the one asking about responders hand. That makes no sence. 1NT is a defined bid, therefor, responder should be asking and suggest contracts to be played, and if you have to many relays you will find it hard to understand what is ment with a transfer bid to any, if you get interference from opponents. Todays bidding is aggressiv, that means that opponents bid like crazy when you open 1NT, since they have all kinds of defence against 1NT. So the best thing is to have all bids defined as something straight away, that way you dont have to guess or be unsecure about the meaning of a bid