If you have all iMessage users, then you can do things like add more users to the chat, etc.
As soon as one Android user is in the chat, then you can't do that.
The other issue, for me, personally, is that I can respond to my iOS users from my desktop (where I spend most of my time), but I have to actually pick up the phone to communicate with my Android friends.
It's not the end of the world, as my Apple Watch tells me when I get texts from my phone, but it is a bit annoying.
If you have all iMessage users, then you can do things like add more users to the chat, etc.
As soon as one Android user is in the chat, then you can't do that.
The other issue, for me, personally, is that I can respond to my iOS users from my desktop (where I spend most of my time), but I have to actually pick up the phone to communicate with my Android friends.
It's not the end of the world, as my Apple Watch tells me when I get texts from my phone, but it is a bit annoying.