I understand the title probably raises some red flags, but this suggestion is not in an effort to promote using the same credentials with multiple vendors or service providers. In some environments, there is a business need to use a set of credentials across multiple domains.
Example 1: In many organizations, AD credentials are used across multiple domains. The current lastpass implementation would require me to save an entry into lastpass for every page or product that might prompt for AD credentials.
Example 2: In a similar vein, at our organization, we engineer networks for customers all over the country. We never know from day to day which device we might need to log into (https://device_ip). A secure set of credentials exists for these devices for different groups within the organization and it is not practical to maintain individual sets of credentials on a per user, per device basis for each device type (fortigate, cisco router, etc).
Being able to right click on a login field and select a credential from a set of 'favorites' or similar in the lastpass context menu would make Lastpass easier to use across the entire organization.