Aerodynamic jerseys are not just for racers.   They are for cyclists that want to cut the wind and go faster.  Here are some basic questions and answers

At what speed does aerodynamics kick in?   

Wind resistance is at all speeds but goes up with the faster you go.  When you ride at over 15 miles an hour on a flat,  most of your energy is used fighting drag from air.   There is much more drag as you move into the 19-22 miles per hour range.

Would you recommend baggy jerseys for long distance riding?

No.   All that extra flapping you feel is draining power from you.   Some mountain bikers can get away with it if most of their riding is below 15 miles an hour.    But on the road, baggy jerseys are a drag.  Literally!

Is there a jersey cuts I should avoid for better aerodynamics?

First lets assume that you are not very overweight.   In that case,  avoid the relaxed fit jerseys some companies sell. These are marketed under different names but the key is they have extra room around the waist that will flap around.  Also the cheap Chinese counterfeit jerseys tend to come in box shaped cut so personally I would avoid those as well.

What are the features I should look for better aerodynamics?

The Professional teams have been wind tunnel testing gear for years and high end manufactures like Nalini and ALE' have been incorporating their learning into jerseys for everyday cyclists with features like:

• Trim or Aero (tight) fit to reduce flapping
• Hidden front zipper to route air away from the teeth
• Longer and tighter sleeves that reduce flapping at the biceps
• Eliminating seams at key drag points
• Special materials that route air better or have less drag

A good example would be the ALE' Speed Fondo Aero Jersey.

What makes you an expert of this topic?

I am but a humble, middle of the pack cyclist.   But I have been riding for 50 years, selling cycling clothes for 20 and worked at NASA on wind tunnel models for a brief time.