Milimeter is close to smallest unit useful in human scale - when you try to draw 0.5 milimeter scale with a regular pen, for example, the lines will probably touch each other. You can't cut with regular tools with better than 1mm accuracy, too. Tools are commonly scaled in milimeters, and you can almost use 14 key for 13 screw etc, so no point in smaller units for regular mechanics work either.
Food stuff is bought in "dekos" (dekagrams). You say "10 deko of this meat, 40 deko of that cheese, and 1 kilo of these berries, please". Somehow hektagram haven't caught up.
Land is measured in ar (10x10 meters), hektar (100x100 meters) and squared kilometers for anything bigger. Flats are measured in squared meters (50-300 m2 for most flats).
1 kg of water (and most other common liquids, with precision good enough for cooking etc) is 1 liter, everybody know that and use them interchangeably. 1 glass is 250 ml is 250 g of most liquids and powders, people measure stuff with glasses when cooking assuming 1 glass = 250 g.
There's a joke about this 1 liter = 1kg assumption. When asked what's 10 times 100g everybody answered 1kg except Russian and Polish who answered 1 liter (because shot glasses of alcohol in pubs are sold as 100g).
1 meter is almost exactly 1 step, 1 km is how far you can walk in 10 minutes.
I don't think one system is better than another in everyday usage, except the much easier calculations in metric.