In regards to DigitalOcean's load balancing other providers often have a free tier so they have to have a version of load balancing (or routing) built out to direct requests to containers that are spun up to execute your code. With DigitalOcean it's for running deployment apps and we currently do not have a free tier. As such the load balancing there is really meant to distribute load either for redundancy or because a single Droplet is no longer efficient at handling the level of traffic you are receiving.
So that $10/mo load balancer gets you a dedicated pair of DigitalOcean load balancer droplets that are just yours and no one else's and can be configured for load balancing. You need a pair, because if one goes down, that is where your traffic is routed so your site would be offline. So by having two you get redundancy immediately.
I would say that unless you have a significant amount of traffic load balancing isn't really necessary.
And while redundancy is great, remember that anything you add, adds technical complexity, and also introduces other failure states. So while it does at redundancy it also adds overhead of management as other services can now fail.