How mixing it up can't be the best way I just can't fathom - as long as you do mix it up to a sufficient degree of randomness, of course.

Just raising the same each time may give your opposition no information - but there are times when you *want* them to have information, which can either be real or false. If you mix *these* up, then you've added an extra level of confusion.

If you raise the same each time, you may not give info but you do provide your opponent with predictability - he can work out his odds against you better, he can get an idea of how much you invest from each position etc. etc. It's a marginal disadvantage, I'm sure, but poker's all about the margins.