It brings it into line with what the other confederations do.
e.g., Venezuela, Togo, Canada and UAE will rarely qualify for a World Cup with the amount of places available (5 or 6), perhaps once in 50 years they can expect to qualify.
But their 'local' confederation tournament is either a 12 or 16 team affair, so another 8 teams can qualify and the teams I listed now have a realistic chance of qualifying for tournaments (or guaranteed in Venezuelas case).
UEFA, at this moment has a tournament with either 14 or 15 qualification places, basically identical to the World Cup (13 places for UEFA).
So increasing it to 24 teams means that teams like Cyprus, Faroes, Finland, Wales, Lithuania, Armenia etc now have a realistic chance of qualifying for a tournament if they make some investment in playing resources, which is surely a case of UEFA correctly looking after its members.
No-one can argue that there won't be a reduction in quality, but I think its clearly a fundamanetally good thing for football in Europe in the lesser tiers. It gives another 20 teams a realistic chance.