Dennis, maybe I wasn't clear enough about why I haven't decided to delete it or not.
It's not about *me* having to check its content in case some app had a problem. It's about not knowing how *Vista* deals with it or its content.
Whether I run into some problem with some app or not, I don't think I would remember to check its content, specially if this log is so big. Even if this file is "just" a log, I don't know if Vista would *need* it (or its content) in some procedure related to apps. As I already mentioned, there are contradict recommendations about it.
Now Marmite and Hazelnut, about the reason to delete this log, or why this log is bothering me, is because it seems to keep rapidly growing and growing. If not now, with its 100's MB, eventually its size will get to the point I will have to deal with this issue.
I will keep searching as suggested. In the meantime, the question about CCleaner not offering to clean this setupapi.app.log is still relevant.
Since CCleaner is offering the possibility to clean other Windows' logs, I thought maybe the devs already evaluated the possibility to include this one (which in most cases will be the biggest Vista's log file, by far). If the devs could comment about that, maybe their comments could point, me and other Vista's users, to a real answer about the usefulness of this log.
In this context, by "usefulness" I mean the use that *Vista* does, or *Vista's* needs (as oppose to the user manually dealing with its content, which I'm not interested in right now in this topic).
To be perfectly clear, I'm not doubting about me needing this log. It's about Vista (or the installed apps) needing it. If there are no consequences in that sense, any user could delete it and CCleaner could offer that possibility.
If the devs don't really know about this log, then I guess adding it could potentially be a suggestion (or at least to evaluate the consequences of deleting it).
Thank you.