I cannot quite understand what this means. Does it limit you in viewing forum pages or it just limits the menber of pages shown to you simultaneously? Can anyone give an example (link) to understand this:

$viewpagelim=50; Max pages you can view in either search, posts or topics list.

Thanks in advance!

Here you go, an example:
use the search facility and look up minibb and set the time frame (Within last... days) to 1000. You will then see the maximum number of pages of results that match the search.
All the best -
mb

Moony
This is also limitation of general displaying splitting pages, for example, on topics list.

Can it affect the work of the forum if I set this to 5000000 for example?

I think, no. I am afraid you will not reach this amount within your life :)

How popular your forum must be, Moony! :) Even if there are millions of posts, is it practical to set the view page limit to anything greater than say, a hundred? There probably aren't many people (if any) who have the time and the patience to browse through a hundred pages of topic/post listings or that many pages of search results listings.
All the best -
mb

I even think - if you have 5,000,000+ posts - miniBB is not the right solution here.