Some are designed as mops, others as finely pointed rounds. They won't hold their shape but are still quite popular with some watercolourists. Test for brush quality by wetting the brush and dragging it lightly across your thumb. It should spring back neatly. Test a round brush for a quality point by wetting it and painting a fine line with it.
Brushes come in various shapes.
Rounds are useful for many applications, including flower painting. Flats are used for architectural type work, for depicting straight edged objects and for painting a thin, fine line if used vertically eg when laying in a yacht's mast. A rigger brush can be added if you want to specialise in landscape work or to add calligraphic touches to your painting. Another popular brush is the hake, which is very wide and flat and is used for large-brush painting in a broad, free style. The choice is yours and to help you with it here is a list of the currently most favoured brushes in the three main categories - as recommended by a variety of Aquanet artists.