I find them useful especially as a reaction to someone else's post, in systems that support this, such as Slack:
1) you can post encouragement/reaction without starting a conversation
2) it's easier for an Aspie to fake normal reactions with emojis (if everyone's using them) than with actual text, which can be helpful in work environments

But: beware that the emoji you type on your Apple device may be different when your friend sees it on their Android device (unconfirmed, but suspected), and/or the vocabulary available won't match, and the names often totally fail to match what the picture suggests to me. So maybe you aren't "saying" quite what you intended.