A fixed departure is fine for a beach holiday. It's fine for a first, easy trek, or a few days away with a crowd. But trekking in the Himalayas isn't a vacation. It's a ritual. It's a spirit. It's time spent talking to yourself, and giving value to yourself. And when you give yourself value, you don't compromise.
If what you want is the buzz of a big, loud group, a fixed departure, or a good night out, will give you that. The Himalayas give you something else, and it only comes when the noise drops away.
Go alone, and you'll find a feeling you'll want more of for the rest of your life. Go with just one other person, your best friend, your brother or sister, your partner, your son or daughter, and you understand more than the Himalayas: the value of life, of the people you love, and of yourself. With that much quiet around you, you talk to yourself a great deal. Somewhere on the trail, you meet your own soul.
The Himalayas are a place of worship. You don't go there in a noisy group of twenty, twenty-five or thirty strangers just because it costs less. You don't compromise on what matters to you as a person, or on what you want from the mountains.