It tells me nothing about the urgency of the matter, let alone what it relates to. So I can put it to the side and keep working - but it's going to be nagging at me "hmm, what if it's about x?".
So now I've got to break focus and waste time just to find out how important it is, and what it even relates to.
I much prefer "Hi, I have a question regarding how to x, could you ping me when you get a chance pls?", or "Hi, we've got an urgent problem with x, the customer is losing their shit, pls help ASAP!"
The absolute worst is when the person giving you "hello" is someone you don't know (I work at a megacorp). From "hello" I will plainly have no clue what you want, so wtf?!
I wonder if it's a cultural thing. I don't think my colleague in the UK, Norway or Europe have ever done this, but it seems to be just about the only way my colleagues in India start a chat?