It all depends on what you want to appear on your report. If you want to show records without X, then the link to the table containing X has to be a left outer join, but if you only want to show records with X you can leave it as an inner join.
For example, if you are doing a proposal pipeline, you only want to include constituents that have (active) proposals. You can safely leave that as an inner join.
On the other hand, you may want to do a prospect report that includes proposals. You want all prospects whether they have proposals or not, so you need to make the link to proposals a left outer join.
If you include the spouse on any of your reports, you will almost always want to make that a left outer join. Otherwise you will only get constituents with spouses.
On the other hand, everybody has a preferred address (even if all of the address info is blank), so there is no need to change that link to a left outer join.
If you are running your reports from a
BB export, you will never run into a problem by making all of your joins left outer joins, so if you are unsure, change it to a left outer join. This will also hold true for reports based on most other data sources, but I cannot guarantee that it will be true in all cases.
Drew