Very little is said on the merits of a really good paint brush. There are many reasons for this, but the biggest one is probably that few people really care about just how good different brushes can be as, ultimately, they all do a very similar job.
However, the very best brush will actually offer a far superior job to a cheaper option and to get the very best, there will only usually be a small extra cost.

It may seem odd to spend more on an item as frivolous as a paint brush, but the benefits a more expensive brush will bring will make that extra investment extremely worthwhile. Not only will the end result be far better, even to the untrained eye, but the time spent doing the job will actually be reduced too.
The best brushes will hold far more paint in their bristles meaning that far less time is spent reloading the brush and that areas can be done in more fluid movements rather than in very sporadic ones. They will also simply be more comfortable, meaning you won’t feel the need to take breaks as often and making the act of decorating far more pleasurable.

For many, paint brushes are things that will only see the light of day now and again, and unless you are very intent on getting the best look every single time, then a normal brush might suffice.
However, for those who like to keep on top of DIY or who need paint brushes as a part of their day to day work, spending that extra money will not only mean that you get a better job done, and finish the job quicker, but you will also probably end up saving money in the long run too, as the more expensive purchases will simply last longer.