Most toilet systems mix the pee and poo together creating a dangerous sewage gloop. Bacteria that thrive in an airless environment (anaerobic bacteria) feed on this gloop and generate gasses that smell very bad. Cassette and pump-out toilets suffer badly from this problem and need strongly scented chemicals to cover it up, which is not great for anyone.
When you keep the pee and poo apart you have two simpler ‘products’. Urine can start to smell after 4-5 days but can easily be disposed of down toilets, drain, grass etc. Poo can be covered in sawdust which helps to dry it and also neutralises the smell. Poo can be easily composted or ‘bagged & binned’.