Some websites require a minimum number of characters from a specific set of symbols which must be included. For example: 2 minimum from [~@#$%] (or some other arbitrary subset of keyboard symbols) + 2 digits minimum + upper and lower case letters with the minimum password length of 12. This extension allows you to set these kinds of rules for the passwords it generates.

You can also exclude some letters you do not like. I typically exclude letters/numbers/symbols which look similar [oO0Il1|] when I must manually type them in for sites which prevent copy and pasting from a password vault to their password field.