What is your area. You didn't say.

There are 2 obvious extremes.
1) Equatorial .
Just place the panel in a horizontal position.
You will get a lot of energy.

2) north or south polar region.
Just place the panel vertical.
You won't get any energy anyway because the sun is always too close to the horizon.

Everywhere in between you just tilt the panel so it faces the midday sun on the equinox.

In most cases it really does not matter much so long as the panel is tilted a bit.

Most places don't get much energy from the sun in winter, so that isn't really an issue. But see above.

That's actually a more complicated question than it might seem at first.

The simple answer for anyone above 23 degrees latitude is to tilt at latitude, so if your house is at 35 degrees latitude, you would tilt at 35 degrees.

However, the best financial payback may be to optimize for summer (latitude + 15 in the northern hemisphere), if you have air conditioning bills that kick up your electric rates into the expensive tier. On the other hand, if you live in an area that gets very hot, the panel efficiency will go down, so it might be better to go latitude + 5 or so.

To optimize for Winter, the simple answer is latitude - 15, but again, not so simple, if there's a chance you'll get snow on the panels.

I have our panels set up so that I could readjust the tilt twice a year if desired, but I have never done so, yet. Too much trouble for a rooftop installation. And I'm concerned about 100 mph wind gusts picking up the panels in winter if I were to tilt them at a high angle. As far as I know, the vast majority of residential installations just follow the slope of the south-facing roof and take what they can get.

If you're talking about water heating panels, I think the general practice is to just match the slope of the roof, and point them southwest (not south) in our area, because that's the optimum balance between the sun and the daytime temperature.

What is the optimum tilt angle for a solar panel in our area? What would the tilt
angle be if you want to optimize your Summer or Winter energy production?