What are the exact benefits of a paid subscription membership compared to normal membership?
Subscribers don’t see the advertising.
Subscribers get profile pictures.
Subscribers get more PM space.
You also have the tingle that comes from supporting the community and doing a good thing, which is priceless.
What about voting in polls?
The polling function is not currently turned on.
What do you mean exactly? 
The polling function in vBulletin is turned off. No one can create polls.
We allowed the polls to be partitioned off to the Russians, Germans and Witnessers. 
Then why are some threads titled “Poll: etc…”?
Anybody can post in those threads. But VBulletin also has a “poll feature”, where somebody can set up polls with preset answers, and other people can answer them, and then VBulletin keeps a running tally of the answers.
That feature isn’t turned on here.
Although the vBulletin poll function is not turned on, that doesn’t prohibit posters from soliciting opinions from others on specific matters.
For example, if I wanted to gather opinions concerning the relative merits of three particular red light districts, I could submit a thread entitled: ‘Poll: Best Red Light District - Amsterdam, Las Vegas, or Gloucestershire’, and all the people on the board who had visited these exotic locations for lewd purposes would hopefully come in and give their considered opinion as to which one was superior. I hope they would give their reasons as well, because I simply have no idea, and I really would like to know.
Anyway I, as the OP, would then have to draw up a chart or something, and record the votes made for each district, calculating the percentages for each manually. If the vBulletin polling function was available, it would do this for me. It might do other things as well, for all I know.
Hope this helps.
On preview: Roughly what Captain Amazing said.
Thank you, one final question, though why is the polling option turned off?
In the bad old days, when the Board was much worse than you can imagine in terms of crashing/shutting down(you truly have to have been here 5-10 years ago), it was thought that it might drag down the functionality of the Board. It still might, we just don’t know.
This has been a discussion topic in the last few months amongst the Mods. It might yet happen. I’m certainly not promising anything. Just saying it’s a topic under discussion.