For several years I mostly rode solo, and I kind of prefer to go solo or with (at most) one or two other people so we can openly communicate about speed, where we're going, if someone needs to stop and do a tack adjustment/fix, whatever.
When you get into bigger groups. . .I don't know, it just seems like there are always problems. People get stupid or inconsiderate. Trail etiquette just gets tossed aside.
Having said that, you take a bigger risk riding solo simply because things can get bad in a hurry, even if it's a trail you know well.
"Parelli horsemanship is just like painting by the numbers. You need absolutely no skill. You just put this color here and this color there, and when you're done, you have ... a mess no one wants." mp