This technique is easy to use and can produce comparable results between years.
However, number counts may show dramatic and unexplained increases and decreases that may be part of a natural cycle rather than indicating species improvement or decline. By doing a number count you will often not gain any insight into why a species has changed, only that it has.
This method can also result in trampling of a population as you complete the count and this can be damaging to the habitat. In some cases the trampling may be beneficial as you suppress competing weeds.
In some cases (such as when a population is large or similar species are present, or the population is spread over a large area) it is possible that some individuals will be missed. Population counts may also be inconsistent between observers as small or non-reproductive individuals may be missed. Where counting is a problem as a result of problems recognising individual plants (for clonal species such as rhizomatous sedges) or the likelihood of missing plants, or double counting, another monitoring method should be used. The accuracy of your count can be determined by using two or more observers that make separate counts and compare results. The difference between the results will give you a margin of error.