In MP, some say it's always recommended. I do it if I have at least one extra fruit tree or berry patch. It's always recommended to assign only one gatherer per berry bush. On 5-berry patches, you'll get: Without Wicker Baskets: ~150 extra food With Wicker Baskets: ~100 extra food. (There are 40 seconds without Wicker Baskets while the technology is being researched.) You can easily distribute the gatherers using the "Order one unit" command. My conclusion is that it's always best to spread out the gatherers. After that, the choice is whether you want food faster or more food in the long run.

It generally pays off in biomes with higher fruit yield like desert or when you have multipe fruit patches

I only research it if there are more berries than just the starting batch.

I wonder if I make a big mistake by never researching the fruit basket tech (basically the only one I don't), given that sources near the CC will be spent fairly fast, I prefer to put my resources anywhere else, and by the time I'm ready to gather other fruit sources I'm already drowning in food from fields... Haven’t tested if the speed difference you mention makes a big difference at the beginning.

Civilians gather food faster from berries and bushes, when compared to the fields. As Romans, you didn't need cavalry against the AI. Cavalry is only useful for hunting and rushes. You need good micro skills for the rushes. Ranged cavalry is much more useful for hunting difficult animals (elephants, bears, etc.)