A coercion dot in not inherently bad and pretty much equivalent to an explicit coercion using one of the conversion functions. Sometimes, you need them but their use should still be minimized to the absolutely necessary.
You should pay close attention to coercion dots, because often things can be improved. For example if you are not careful, multiple coercion steps can occur in sequence, while with an explicit conversion you can be more selective to make sure it only occurs once. (For example, if we need to divide five different DBLs by N in a loop, it is probably more efficient to convert N to DBL right away instead of having a seperate coercion at each division operation.)
Many time, you can also rearrange operations to minimize coercions.
They also alert you that your chose datatype may not be optimal or appropriate for a certain function.
It is always best to avoid coercions/conversions. Choose a proper data type from the beginning if at all possible.