Even worse, sometimes it is used as replacement for instant messaging.

In my view it is not, it is a replacement for mail.

When letters were actually hand written (and - side note - sending them had a cost) the idea was to communicate, you used to sit down at a desk in front of a blank sheet of paper, THINK about what you were wanting to communicate, THEN wrote it in the most correct and concise form possible.

E-mails are very often nowadays yust "Yo"'s, a handy way to either (you choose) annoy someone else for free, or delegating to the recipient the solution of a problem that you could solve yourself if you only take the time to think about it or pestering the recipient with a CC of an otherwise irrelevant mail you just received.

It has a lot of advantages when compared to a phone call (as an example it is he handiest way to send a document or even an address without having to spell over a noisy line) but it is not a SMS (that BTW is good enough to send a telephoine number or an address) but it has also a lot of disadvantages (still as I see it).

When you make a phone call you have some restrictions, the recipient needs to be available, you do know that you are disturbing him/her, possibly interrupting whatever he/she is intent at (and this self-limits - in "normal" people of course - the amount of phone calls made to those actually needed), but it is more personal, you can communicate (tone of voice, etc.) more unwritten nuances, it is interactive, there is less risks of misunderstandings as you or the person you are speaking with can ask for clarifications.

I have seen (in corporate environments) e-mails often used as a form of justification for inactivity, i.e. "I sent xxxx a mail, he disn't respond yet, I cannot do anything till then" (or if you prefer, "It was my problem but I deftly shiftloaded it onto xxxx, now it is his problem"), this is the kind of behaviour that besides slowing down overall the response time in real emergencies, creates a perverse loop, recipient xxxx will be likely to CC the issue to a third person, to have an opinion, etc.

The same (corporate) culture that equates the e-mail to instant messages favours the expectation that the sent e-mail should be replied immediately (and creates a symmetrical sense of guilt to the recipient that feels obliged to reply as soon as possible), and thus the continuous checking of the e-mail boxes, the disrupting of the flow of work by the distractions created, etc.

When someone calls me (at the phone) or enters my office (in person) he/she is disturbing me and interrupting my activities, they perfectly know that, and restrict these interactions to when it is actually needed, otherwise they send me an e-mail and they know that it will be duly processed in due time.