Citation appreciated but not required
David E: They can but that depends on the site. The ads are often large, contain code (this is why they are often very very dangerous, malware) and they may be served by slow servers. Ads generally do NOT come from the same server as the web site.
When you go to a web site, first your browser turns answer.yahoo.com into an IP address with a DNS query. This is why DNS speed testing tools like the one Steve Gibson wrote (https://www.grc.com/dns/benchmark.htm) can be seriously useful. A query that returns immediately rather than half a second later can make the internet seem like it is on turbochargers.
Then the browser gets the text of the page. Adds and often portions of the content are not on the same server so the browser has to go get the IP address of those servers (DNS again!). Then it ask for the ads and the pictures, music, videos, etc. It also runs any code like the can't die fast enough Flash. (No really, Flash is way way way past its life time.)
So, if you don't bother asking for the ads, then you don't need to take time to load them.
Again, this all depends on how the site is implemented. Many like some of yahoo properties are not all that fast to start with. Others are done right so not getting ads is much faster. Espeically if the ad server is a slow one.
Well, no it doesnt and if it does just remove it. besides, better to wait for the web page to load a little longer, then have it load but be impossible to navigate because excess of adds.
Yes, reduce like 0.xx seconds? Website consists of text & images data. advertisements are considered of images data.
if u goes to streaming sites, they relies heavily on advertisements to survive,u can see drastic differences.
Anyway, just test it on yourself with tools.pingdom.com