Why might a point mutation in DNA make a difference in the level of protein's activity?

Point mutations can be very serious because there may be changes that will occur to an organism. Do remember that some mutations will not make too many changes. If there is a small change to the DNA, this will already be considered to be a mutation.

It can be problematic when mutations will affect a larger portion of the organism’s DNA. If an organism’s DNA is changed, something that the organism should have been able to do without any issues cannot be done anymore. The DNA used in order to make this possible will not be there anymore and this can be a problem for sure.