Vertical scaling is much easier because it only refers to scaling with one single server. When your server and its application require more resources, vertical scaling solves this by allocating more resources to your server. With old web hosting companies, this is accomplished by having you upgrade your plan, locking you into a new rate, and incurring significant downtime. With Slicie, your server scales automatically, without a reboot.
Horizontal scaling is much more complicated because it involves many servers. You need to add complexity to your application by allowing it to be distributed across many servers, usually done with containerization, using software like Docker and Kubernetes. While horizontal scaling can handle huge, fortune 500 sized systems, it requires a lot of skilled employees to manage.