There was a time when you had to calibrate certain sensors to get them started, and I think that remains the case with Medtronic proprietary sensors, but not with Tandem or Freestyle. That’s not to say it might not be necessary now and then, so calibrating itself is not bad - it just depends on if it’s actually necessary and what the goal is.
I just upgraded to the G7 about 6 weeks ago and did need to calibrate my very first sensor because my feelings didn’t match the CGM reading and the two numbers were way off - and not just in terms of the numbers themselves but the percentage difference (very important); and when I used the G6 I calibrated it occasionally as well.
When I do a calibration I find that the resulting reading is midway between the CGM number and the fingerstick, which makes sense, and I consider that my new baseline. I’ve heard (not necessarily here 
) that some people want to keep calibrating until the numbers are nearly identical - but I would think that would result in the CGM trying to chase the calibrations rather than reading the numbers from the body.
I’m not a technical person and hope that makes sense - techies such as @joe and @Dennis can no doubt offer better and different explanations, and offer any necessary corrections to my efforts.
Again, calibrating isn’t necessarily wrong - the big question is, is it necessary?
Here’s a link to a discussion on weight loss that contains some discussion of calibrating. Weight Loss and Dexcom correlation? - #3 by Dennis