Some vendors (like Viking Vapor) will sell their flavors in double strength, so that you can cut it down with your own PG/VG. If you can procure your PG/VG in bulk locally, this can save money in the long run. But you can only do that 50/50 without losing flavor so you can't dial it in to any nic strength you want without affecting the flavor.
That's basically what you do at Tasty Vapor.. buy higher mg flavored nic juice and cut it with flavored PG/Vg to make a lower strength.
If you buy the "doubler" at Tasty Vapor, the zero nic liquid is flavored the same as the nic liquid, but at a lower price. This you can use to set the nic level at whatever you want without losing flavor.