I don’t think whom is necessary for effective communication or for practical language use. However, I don’t think many words that are in our lexicon are there because of their practicality - part of language is the beauty and art of language as much as the expedience of it.
I would rather it not be used at all than it be used wrongly by people who are trying to be sophisticated, because then it comes off as a little pretentious. However, in the right context, whom can make a difference to the feel of a sentence. Daily use? Yes, it sounds pretentious or archaic. But in writing, it can add character and change the style.
Consider the following:
There were seven people present, most of whom I knew intimately.
There were seven people present, most of who I knew intimately.
There were seven people present; most of them I knew intimately.
Three sentences. The second one is not grammatically correct (who and whom are not actually always interchangeable.) The first and third are different enough that there are times where one might be preferred over the other - times when whom is still the better choice.
The other place I appreciate understanding how to use “whom” is when I am reading historical documents or praying older prayers/singing hymns. There is a sense of history that comes from reading a word that has largely fallen out of use, and it makes me appreciate the rich history of our language and, through that, the history of whatever document or song I am looking at.
“Whom shall I fear?”
“Whom shall I send?”
“Of whom shall I be afraid?”
It just wouldn’t be the same with “who.”
Prayers are really the only time I use a number of even more archaic words, but I enjoy doing it, I think for the same reason I still enjoy using Latin. There’s a different tone and feel to it when it’s the same words that have been used for hundreds and hundreds of years.
One last note on whom.
If I look at any particular word too long, it stops looking like a word and just starts looking odd. In this particular case, after spending (way too much) time considering the many and varied reasons I am attached to the word whom, it suddenly looked like something different. Like wham, but with an ‘o’. Whooom. Whaahm. Like a sound effect. If I use it as a sound effect in my novel does it count toward my word count?
“Thy kingdom come”