Mh, i'll put my opinion here, since i was considering making a devlog here:
1 - Surely before having an actual realease, it should be a good place to talk about your own project;
2 - After releasing the game, it might become unnecessary... or maybe not: devlogs in the released game page seems more like a place in which to talk about the latest update released or a certain event related to the game, but seems more like a recap of changelog and some text to introduce the update... what i want to say is that here the devlog can be more thorough into the developement process, assets, detailing about creative/design process... all that kind of stuff that maybe doesn't fit well when you want to just say that there's the new latest version of the game to play;
3 - There's also another scenario (like mine): i'm the developer but the publisher created the page of the game, so i cannot write the changelog whenever i want, in my case i should before write it elsewhere, then contact the guy who works for the publisher and that has access to their Itch account to PM him to tell him "Ok, could you please copy-paste my wall of text with Image A, B, C... and oh, Image B must be placed between those 2 paragraphs, and this one instead...", sounds enough an hassle for both already. Obviously i cannot make a post happen at night, if i feel like writing at night (during day i'd rather work on the project itself), and i also have to hope that that guy has some time to make that post when i'd want it, without having to wait when he has some time to do that. In other words, it would be good to write what i want here and main announcements and events on the devlog of my game's page
Sounds reasonable enough?