This argument bothers me a little. These days hosting is cheaper than ever.
If you're starting a new community and you fork out $140 for XF, $30 for a theme and $30 for your first months hosting, that's $200 right there with zero add ons.
You then spend days or weeks tweaking your forum, making it perfect, just right for your niche. It looks beautiful, it's perfect, now you just need the users. Great, you go out, start promoting, people sign up, you get a little initial buzz. But then it starts quieting down, users aren't visiting as often. They're not re-engaging.
Why aren't the conversations flowing as quickly as on other social networks you've been visiting? Why aren't users interacting and with each other as fluidly as on facebook? Why is that facebook group on a similar topic so damn active and thriving compared your beautiful feature rich forum?
Because it's missing some of the key features that are vital for helping smaller communities to grow quickly. Features that are implemented by these big networks because they work and make them a joy to use.
Are you telling me you're happy to spend all that money on forums software and skinning, and all that time and opportunity cost sunk into creating your forum only to skimp on an extra $10 or $20 a month because hosting is too expensive for features such as live update and video upload that will help drive posting and give your forum that extra chance of success?
Or would you rather just take forum software as it is today and give it a go, with a much higher chance of your new site failing because it's missing these features that every other modern web app is using? But hey, at least you saved $20 a month for the 6 months you tried to make your site work and now the site is dead and you have nothing to show. You're cool with that, right?
Large forums with momentum and dedicated user bases don't necessarily need all these features, and yes if you were to make everything live on a big board you'd need some serious freaking hardware. So you should have the option to configure or turn off resource heavy features like that. Many big boards may feel they don't need them at all.
But smaller, newer forums need the option for features like these because users simply expect them, it's what they know and are accustom too on all the big sites they use daily. They really do increase engagement, driving growth at the critical early stages. All this live crap isn't just marketing, it works.
If those features aren't available and newly registered users don't stick around because the software feels outdated and don't have the feature to re engage them promptly using the modern web technologies they've grow accustom too, then they will leave to use facebook groups, subreddits, what's app groups, or any other modern community software provided by the big boys that do utilise these live features, and have polished, fast, reliable feature rich web and mobile apps.
It's the smaller forums that are losing out here and failing. The barrier to entry to create a community based on the hosted codebase of big social media site or other community platform is so low these days, members will just abandon your site and make their own community on one of these other platforms, and likely do pretty well.