It is essential to know what each others plans are for your money. This means what that looks like currently and what are the plans for your money in the future. You want to know that your financial habits and goals are compatible with one another.
For example, if your dream is to be a homeowner, then your goals may be living in an apartment with a roommate or doing away with vacations in order to save money. What does your partner think of this? Or let's say your partner has even more lofty money goals. Will you be able to join him in the sacrifices necessary in order to accomplish them?
Chances are your money goals will not be perfectly aligned at the moment. The key is to know where each of you stands so you can see if you can both happily get behind what the other has set for their financial goals.
Whether you choose to combine finances or not, their money situation is going to affect yours. This is especially true if they are carrying debt. In the end, it all comes down to personal preference. You may find it may be smarter to keep your finances separate.