There is no valid argument for not letting an FO fly every other leg, unless your procedural and regulatory guidance calls for it. (Special airport, monitored approach, etc.) When it occurs, a good Captain will make sure that the FO does not get "cheated" out of their flying. (Giving them another leg to make up for the one they lost.)
You might not be a NetJets pilot if you share the above opinion.
Generally, I will absolutely alternate legs. Occasionally, I will take the next leg depending on the circumstances.
ie...
*Coral Reef Club,
*Aspen on a busy and poor weather day,
*Landing at a back-woods short runway airport on a slick and rainy day with gusty winds.
We don't routinely operate to or from anywhere. We do fly to some airports in higher concentrations, but not with regularity (TEB, PBI, MDW, etc.). There is no opportunity for NJ crews to develop "familiarity" at several airports like a 121 pilot can.
Type rating or not, it's safer for a pilot to see someone else operating in challenging airport environments 1st before taking the controls and operating in them personally (IMHO). This isn't a MAN contest. This is a customer service job.
NJ does not sell "minimum certifications" (FAA APPROVED) to our Owners. NetJets sells higher standards to our Owners in the interests of safety and comfort. It's those couple of notches above "legal" that our Owners pay for and receive. It's called "polish" and we love to give it.
And this isn't a "beat up on the SIC" practice. NetJets doesn't release Captains directly to the line following UPG training for just this reason. New PICs fly as a PSIC for a period of months until they develop a solid operational experience base former from experience, not simulation.
Again, this is a company cultural phenomenon based on saefty and comfort... "polish". It's not a "man contest".