These columns are pretty common around here. They are structural. They hold up heavy roof sections and porches.They are hollow!
These pillars can hold a lot of weight for a long time, as long as water doesn’t get inside. Unfortunately, water frequently does find its way into the middle of these columns. When water gets in, they rot from the inside out.
Do you know what those holes are for now?
Yep! The holes allow the columns to drain. This can extend the life of the columns. Since it is a fairly pricey fix to jack up the porch and replace them, this is a great idea.
When house hunting, look at the bottom of columns like this. If water is puddling inside, the wood at the base will show it. Water will eventually percolate through the wooden base. That base will show it by having flaky paint, or it will have warped, squished, or otherwise misshapen wood.