If your concern is your ISP knowing which genre of porn video you watch on pornhub, you don't need a VPN. This information is already encrypted.
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If your concern is your ISP knowing that you go to pornhub, ..., then a VPN may be beneficial to you.
These two don't quite match because without a VPN your ISP can still see your URLs and that's enough to know what you you're looking at, even if they cant see the specific images you've accessed.
Without a VPN, your ISP can see the base level domain that you visit, but nothing further (assuming https is used).
So it the latter example, if your concern is the ISP knowing that you view porn at all, then a VPN will be prevent your ISP from seeing that you went to "pornhub(dot)com"
But if you don't care that your ISP sees that you watch porn, but really don't want them to know that you watch interracial tranny porn, then you don't need a VPN, like the former example. Your ISP will see that you went to pornhub(dot)com, and they'll see how much data you streamed from there, but they wont' know what you streamed from there, or the exact URL to the videos you watched. This information is already encrypted as is (https).
But again, anything that the ISP sees can now be seen by the VPN provider when you use it. So if your concern is nobody being able to find out that you watch porn on pornhub(dot)com, a VPN won't do you any good.
EDIT: I reread your response and I think I see where you confusion is:
With https and no VPN, your ISP can see that you went to "https://www.youtube.com" but cannot see that you went specifically to "https://www.youtube.com/watch?v=GHoqIa1TJ9w" That part after the slash is not visible to your ISP as long as https is used. They can only see the base level domain.
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These two don't quite match because without a VPN your ISP can still see your URLs and that's enough to know what you you're looking at, even if they cant see the specific images you've accessed.
Read them carefully.
Without a VPN, your ISP can see the base level domain that you visit, but nothing further (assuming https is used).
So it the latter example, if your concern is the ISP knowing that you view porn at all, then a VPN will be prevent your ISP from seeing that you went to "pornhub(dot)com"
But if you don't care that your ISP sees that you watch porn, but really don't want them to know that you watch interracial tranny porn, then you don't need a VPN, like the former example. Your ISP will see that you went to pornhub(dot)com, and they'll see how much data you streamed from there, but they wont' know what you streamed from there, or the exact URL to the videos you watched. This information is already encrypted as is (https).
But again, anything that the ISP sees can now be seen by the VPN provider when you use it. So if your concern is nobody being able to find out that you watch porn on pornhub(dot)com, a VPN won't do you any good.
EDIT: I reread your response and I think I see where you confusion is:
With https and no VPN, your ISP can see that you went to "https://www.youtube.com" but cannot see that you went specifically to "https://www.youtube.com/watch?v=GHoqIa1TJ9w" That part after the slash is not visible to your ISP as long as https is used. They can only see the base level domain.
and if the isp is selling to google... that can also be a concern for some people.