I like them!
Whenever someone subs me I check out their profile first to see if they're also a creator, because I've found a lot of great artists and series that way. I'll peek at their wall and sometimes I'll spot some art that catches my eye, and check that out too. Or I'll see the same thank you on several of my followers' walls. If that many people who like my stuff also like THAT thing, there's a decent chance I'll like that thing, too.
And then I'll post a thank you image, first because I really am grateful for all my subs, and also to keep that share culture going. I feel like it's a fun and harmless way to help people find series that interest them, without like...going into their reading list.
The only time I won't is if their wall won't let me (naturally) or if their reading list is hidden.