The sending talks upfront section is a little dismissive

[cedmax]

Sometimes conference organisers ask for the talk because they have live translation (either in another language or to sign language) or such and it does help a lot the translator to know at least what to expect. It doesn't mean the slides can't ever change, it's to give some guidance instead of forcing them to wing it

[brentvatne]

Perhaps not entirely the intent of this point, but sometimes organizers also want to do a practice session or two with speakers beforehand. This is valuable from the organizer's point of view to mitigate the risk of unprepared talks, and from the speaker's point of view it is an earlier deadline to have the talk prepared for by, without the pressure of it having to be 100% complete and polished. I would recommend this for every conference if the organizers have time. This is kind of a sub-case of sending talks upfront.