bug#57804: An infinite loop in a `fontify-region' function causes Emacs to hang indefinitely

[Gregory Heytings]

> How do I decide what is sufficiently large? With this optimization 
> Logview can fall into that infloop in fontification code, at which point 
> Emacs becomes completely frozen, with the only way out to restart it.

You just described what would happen without this optimization with a 
sufficiently long line.

> With long lines I can suffer slow and not-quite-responsive (but still 
> not hung to death) Emacs, which is much more bearable.

Obviously you did not have to deal with long enough lines.

> For you this long-line optimization is probably very important, maybe 
> you often work with files that trigger this and make using Emacs a pain 
> without it.

It isn't for me personally, no.  It is important for Emacs users.