My daily meds for asthma and allergies tend to suppress my appetite, so I need to weight myself once in awhile. Usually once a week or so. More often recently. I'm trying to keep my weight up to around 160.
When it dips lower it's usually a sign of under-eating, illness or dehydration. In the past when it's dropped to 155 I had a low grade infection that went unnoticed for awhile -- tooth, sinuses, etc.
If it goes up a bit to 165 I don't worry. It'll come down again with moderate exercise. As long as it doesn't go above 175 I'm not worried. The most I've ever weighed was 205, and that was after a car wreck busted up my back and neck enough that I could barely move for a couple of years. The weight came down again as soon as I changed my diet a little and began walking with a cane. Now that I'm back on the bike it's easy to keep the weight off.
Just a lucky roll of the dice genetically. I know some folks who don't overeat and struggle a bit to keep off the weight.