I have tried a couple of different projects, here is what worked and not for me.
VA managing social media
I tried working with a US agency to manage social media, it didn´t work out very well and was quite expensive. They did post things on social media but I had to spend a lot of time managing and correcting things. I didn´t feel they were taking responsibility for what they were posting, just using automation tools and guess work.
$200-$300 / m for a few tweets/fb posts per week of which many needed correction, I only run it for a few months when I got started.
SEO checkup on site
This worked very well with a resource from Pakistan, I don´t remember the total cost but a few hours at $5-$10 / h for a few h. I got a full cleanup of the site, no visual changes, just fix things behind the scenes in the html, a follow up call explaining what they have done and what´s left to do which may incur visual changes. Just backup before you let them in and you are safe to go.
AdWords campaign optimization
I wanted to learn about AdWords and try out running campaigns. I setup a campaign and quite soon found myself spending far too many hours watching videos and reading up on how to optimize a campaign on general level.
I hired a resource from Bangladesh at $8 / h, he spent 3h changing all the settings and wrote a 3 page report with screenshots and all explaining all the changes. I got the campaign fixed and I learned a lot from the report as well.
So in my experience it´s been successful with very specific tasks, VA didn´t work out at all.