I don't think that it's sitting that kills. I think it's more the fact that you are less active. You can have the same problem standing all day without moving around.
I have worked on several projects that successfully used MongoDB over the past six or seven years now with three different companies. One project had over 5TB of data spread out over a couple of databases with numerous collections each, and no we didn't shard that database. We also didn't have any issues with accessing the data at that size. When I see negative stories around a technology, especially databases/data storage, I personally like to dig in to see if things are as bad as people say. All platforms can have issues (don't get me started on SQL Server and torn pages ;) ). Most of the negative press I've seen around MongoDB was from people not understanding the technology. Sure there were valid issues/bugs and some people might have lost data, but I don't think it was as widespread as some posts would have you believe (except for those running old versions accessible from the internet without proper authentication that is). Also a lot of posts that keep coming up are from several years back. MongoDB has changed a lot over the past couple years, and they continue improving the platform with each release. Bottom line, understand the platform before using it, learn it's strengths and weaknesses and you should have a successful implementation as well.
MongoDB Atlas which was already a great product just continues to get better.
My favorite on this list is being able to restore a subset of data from a queryable snapshot. This will be a time saver for those times someone accidentally drops/updates a few documents and they need to be restored.