I own a 2014 4GB/128GB 11" MBA and have used it on-the-go for everything that I use my iMac for. I render video, I edit/create graphics, run virtual machines, etc. It is quite a little beast... runs macOS Sierra extremely well and is just as snappy as the day I first bought it.
One reason I didn't opt for the 8GB RAM was because (a) it wasn't going to be my primary machine and (b) because of the price I paid for the 4GB model, $475 brand new out-the-door-taxes-included, the additional $200 to bump it up to 8GB was a bit excessive IMO.
If you plan on heavily using the MBA and keeping it a long time, I'd recommend going for the 8GB model.