Having an extra profile open doesnt really make a lot of difference to battery use. Its more down to what apps are running. (Also the quality of your network connection can make a big difference!!)
If you have Google Play Services installed in multiple user profiles it will have a significantly higher power draw than if everything was just installed in one user profile.
Using secondary user profiles can be very useful if you want/need to be able isolate apps/groups of apps, keep some data/apps encrypted while still being able to use the phone (dont unlock or end session a user), reliably delete data (delete a user), quickly completely shut down a group of apps etc.
Working between user profile is more of a fiddle than doing everything in one user.