Is it needed? No
Universities usually only make offers based on 3 A level grades.
By doing 4 you leave yourself vulnerable for them to "pick" the 3 subjects you need to achieve a grade in.
E.g. If you were doing English, Maths, History, Business Studies
They may give you an offer of BBB but they may specify that you need these three grades in English, Maths, History
You would then be stuck doing an extra a level (that you may need for other unis) and this may bring all your results down as a result.
Better to get 3 good grades than 4 mediocre ones.