One has the expectation of an almost immediate response, while the other has the expectation to be entirely ignored until someone brings it up in a meeting a month later
I'm the BI guy on my company, and everytime someone new come in it ask me via chat the address from the different BI dashboards and I always ask them to bookmark the pages and don't rely on the chat history because for corporate policies it's auto delete ever so and so.
Personally, I would only use email when I don't need an immediate response. IM is for "I need answers and I need them right now" kinda shit. And if I ain't getting a response fast enough, I have to resort to shudder actually calling someone.
Unless it's an open protocol behind it, it will never completely replace email. There will always be a Slack / Google Chat willing to take some market share and force people to still maintain email accounts.
The main difference for me, is that I refuse to use the IM.
I have email for text, I have an office phone for voice, and I have a cell phone for voice & text.
No. I don't need to keep a separate browser window open just because someone might want to use a different system that does the same thing.
I even set a permanent away message that says "I will never see this, send me an email." But every now and then I still get an email alert that I have an unread IM from 2 weeks ago.
EDIT: I'm guessing the downvotes are from the people who are still waiting for an IM response. 🤷🏻♂️
I get it but I don't. If I am on the factory floor and need someone to be where I am the IM is the best way. If I call they could be away from their desk or not in a position to get a phone call. If I email it might not get their attention.