While a regular chair might feel fine for just the first hour, it often leads to some shifting if you are fidgeting or even slouching. Even the hours do pass, an ergonomic chair stays comfortable.
The chair gives support for your body evenly. Because of this, pressure on any single area is lessened. That means that your legs feel a bit less numb, and your shoulders cramp to a lesser degree, and you are much more stable throughout the day. You stay more focused so relaxed throughout work or study because you’re not constantly repositioning.
Many people describe sitting in an ergonomic chair as “balanced” or “weightless”. It simply holds you in just the right place it doesn’t pull you either in or push you further forward. Adjusting to that feeling may require time. It is difficult returning to a normal chair then.