To be honest there are only 3 reasons when to use managed services:You do not know any better You are too lazy It is cheaper (rarely; only for enterprises commonly)
Using NodeBB's managed service would cost me 750$ just for my forum alone. Not even to mention "side" applications like a CMS or a few static HTML pages.
If I would count the traffic costs in (DO based calculation) the plan wouldn't be affordable for me.
Assuming I just need the +5M PV plan for 750$ it still would mean that I pay more than 720-730$ more than for my current system, while losing many benefits of a dedicated setup.
Another example, imagine I would have NodeBB on all my sites and those I manage (+90). Sometimes a rented server might not be an option anymore. Maybe you want more scalability and therefore actually need a cloud server, but it is too expensive. Or maybe it is sensitive data which you want to keep out of the cloud for security reasons.
Lets take it even further. Despite the massive one time costs a server brings, you will even have to hire someone to monitor that one machine (usually you use a cluster, so you actually have +2 machines). Now you could have costs of approximately 3500-5000$ compared to 750$.
Sure in the above case with multiple sites you would have to take 750*90. But imagine you have one big site with the same amount of visitors. Then it makes sense and actually saves you tons of ash.
Some might ask himself now:
"Why don't you do it better then?"
First of all I am not that desperate for cash, second I won't be the dickface who steals useful funds.