I really don't think that advice applies any more. It used to be that you could see ranking changes pretty quickly, and by making one change at a time you learned about what change had what effect. But Google today is a lot more complex - with ranking changes bubbling up and down over time, even though the actual cause may have occurred at one specific time.
I know that I personally dropped that one change at a time approach a while ago. If you're making basic, on-page changes, then there still might be something to say in favor of one at a time. But most of the sites I work with are making all kinds of changes all the time anyway - there's just no time built into that process to wait around!
That said, if I need to change the URL structure, the entire main menu, or something really major like that, then I would definitely carve out a period of say 2 weeks or so to launch the change and watch at least the first layer of effects.
I read pretty recently that Google was temporarily dropping the rank of pages that had their title tag changed. Is that still happening
Whenever I want to do that, then if it's a site that doesn't get much updating normally I usually make a small change to the on-page text to try and give some back-up to the Tag change. If it's a regularly updated site, then I don't always do the back-up change.
Yes - it's not happening always in every case. But it does happen often enough to be aware of the possibility. I'm assuming it's a kind of protection against title changes made only for SEO purposes or to try to reverse engineer part of the algorithm.
Well i changed all my titles on all pages of ons site(because i thought these titles might look spammy in the eye of google animals) a month ago, and now you tell me it wasn't wise? Now in this situation: change it back or leave it as it is?
I could be wrong, but I was under the impression that if there were a ranking drop it would be right away and then slowly come up to the appropriate spot. If you made your changes a month ago, I think you've already ridden out any potential trouble.