Wi-fi offloading is what Republic is all about. The phone is a "hybrid" phone, able to make and receive calls using VoIP over wi-fi as well as over a cellular network. Using an available wi-fi connection to make and receive calls reduces the demand for cellular bandwidth, which is much more expensive than wi-fi bandwidth, since wi-fi bandwidth doesn't cost Republic anything.
Wi-fi offloading is why the monthly cost of the service is so low, which is what attracted you to the service in the first place. If you care about keeping the cost of the service low, then you should care about offloading as much of your usage to wi-fi as possible. If you don't use wi-fi at all, then you're essentially a leech, because you're not contributing to the principal of helping to keep the cost of service the lowest in the industry.
If you disable the cellular radio (with Airplane mode) and toggle on wi-fi only, your battery will last much longer, and you may find that your wi-fi calls are of a higher sound quality than cellular.
Don't take the wifi offload numbers you see in your account too seriously. They are interesting to follow, but are not an accurate measure of the "burden" your cell usage is placing on the system. For example, you can use 1000 cell minutes and have a wifi offload of 80% (which looks great), or use only 10 minutes and have a wifi offload of 10% (which doesn't look so hot). In that comparison, the 80% offload looks like the better case, but actually uses a lot more resources.
Just use wifi when you can, and you're good.