I can only speak for myself.......but like Dale, I wanted as much good land (not desert or swamp) as I could afford to buy and pay the annual taxes on. I ended up with 21 acres. I would have preferred 40 to 100 for the elbow room and privacy, but we didn't have the cash to do that unless it was trash land, which I didn't see the sense in buying. And I didn't want to go into debt. That was important to us---no mortgage. If things went poorly, I don't want to lose our land to foreclosure.
I actively farm 6 of those acres in food crops mixed with high quality pasture for the sheep and goats. One acre is for residential use (house & driveway, solar array, dog yards, cat sanctuary). The rest of the acreage is in lower quality, treed pasture & mixed food forest.
Our 21 acres gives us just about everything we need for a fairly self reliant homestead...... enough pasture for assorted livestock, gardens for annuals & perennials, space for compost production, trees for firewood/limber/posts, space for farm buildings, room for a plant nursery, the ability to grow tons of assorted biomass for mulch and compost. Plus room for numerous ponds for fish and water storage. Plus plenty of room that if I make mistakes it's not a disaster.
Without the livestock, I would be ok with having less acres. But my mental health significantly benefits from the space around me separating me from my neighbors. 20 acres seems to give me the space I need. So even without the livestock, I want the added acres.