For instance it can be a love spirit that is great at baneful magick, or a spirit of science that is also great for wealth etc. It can be anything really.
But I hold the view that everyone gets too see different sides of these spirits of the Goetia and or other grimoires.
You can always ask, but generally people on here report poor results when they ask an entity to do something outside their offices. But it depends on the entity. Belial seems particularly prone to this, but others are more flexible, like Lucifer is the Swiss Army Knife of entities and you can ask him to do almost anything.
like mullberry said , there can really be some spirits that are more flexible . i think that they can be more flexible with you specifically if you , as a person , feel or have some kind of connection towards them . personally , my patron helped me with many things outside of His domains , which usually only cover music , philosophy and necromancy . He helped me with feeling more happy and motivated , taking care of myself and just becoming as good of a person as i can be . and i think a reason for that might be because of the connection i felt towards Him .