This is something often overlooked completely.
Many time I've been told there is no need for a long Yagi on 4M or 6M and that a dipole, or even a vertical, is good enough.
The argument being that when the bands are open with ES the signals will be very strong.
Often very true.
You cannot work the stations you want to because of strong signals from another direction.
A good beam saves the day.
In addition, if you live in a noisy location, at least the yagi reduces the signals from the unwanted directions.
Now tropo is different again.
Then you really do need as many elements as possible.