Sometimes though, people can retain bad habits in ukemi if there is not enough practise 'cos the Nage is usually concentrating on their technique too much to notice these in the uke.
For example, it is common for beginners not to use their knee when rising from a forward ukemi, but to roll up using both feet (which is maybe more comfotable, but gives a less stable rising position, should you be attacked while rising). Reverse ukemis are often done on the wrong leg during a throw as well (making it less comfortable).
Also, many people (myself included) have a tendency to break-fall rather than ukemi. Excessive use of the break-fall tends to make you feel very dizzy after a few days of practise (due to the shock of the fall). Being confident in ukemi and only breakfalling when absolutely necessary is beneficial.
To me ukemi is very important 'cos its about keeping your center.