There are several factors to consider here:
1. I make up gelatin at 20% and 10% in advance for storage to reduce darkroom prep time. The preservative is useful here. I can keep preserved gelatin for 6 months or so and hope to increase this to a year or so soon with a wider range of preservatives.
2. Anyone who knows biology, knows that gelatin is a good growth medium for all sorts of micro-organisms. We are warned not to work with our emulsions and gelatin solutions if we have a cough or strep or any form of illness like that. This can "turn" an emulsion or gelatin just about overnight.
3. The experiments that I showed at several of my workshops were from emulsions up to 6 months old and the coatings were over 1 year old. Curve shape looked pretty good to me. I could not have kept the emulsions for 6 months or more without thymol.
4. I make my standard emulsions in 120 - 500 gram batches and often mix them, they are so much alike. I keep a 1 L can of the blends for my common coating checks to refer back to when I make experiments. If I don't know where I have been, I don't know where I am going!
5. Finally, use of Thymol or any preservative is useful, as you then have a coating formula which includes this chemical and therefore does not need a big change when you change workflow to included older emulsions and gelatin solutions.
This all summarizes why I teach the use of preservatives in my workshops!