Releasing all lecture materials at once vs. releasing materials lecture by lecture
As a CS student, I experienced both types. In my opinion, there are many practical disadvantages and psychological effects to consider when releasing everything at the beginning of the semester. 

However, it is very nice to be able to view the materials from previous years in full, and almost none of the disadvantages listed below apply for this case.

Practical considerations:


If everything is available at the beginning of semester, students might deem it not necessary to check the course website during the semester, as they already know that "everything is there". They will miss announcements and updates to the website.
If the lecture materials are changed or revised during the semester, students might miss these updates if they downloaded everything at the beginning of the semester.


Psychological effects:


Information overload: Students may think that the course will be too difficult if they take a look at later slides at the beginning of the semester and thus might drop the course.
Frustration: Eager students may try to understand the contents of later slides (e.g. a few weeks in advance), but get frustrated if the slides are not completely self-contained and there is information missing (that would have been given in the lectures).
Lazyness: If everything is there at the beginning of the semester, students may not feel the need to keep up with homework/reading week by week, as there is less of a weekly reminder that things have changed (the page is static and does not change every week). If the materials are released weekly, there is more of a motivation to not fall too far behind, as students are reminded every week of how far behind they are. Also, students might not be motivated to go to the lecture if they already know that all the material has been released.
Inattentiveness: Students that have already read the slides of the coming weeks may be bored or inattentive during the lectures. This may be important if the slides "give away" too much of the thought process if students read ahead. In some lectures, homework is only mentally stimulating if the slides of next weeks' lecture are not available in advance.
Students may also get the impression that the professor is just "phoning it in" for this year, even if that is not the case. If slides are released every week, this gives more of an impression that the lecture was tailored to this specific year, and to the questions asked during this year's lectures.