There are some interrogatories that you have to ask in every case--the identity of the persons with knowlege, for example, and the identity of the experts. But if you are representing a plaintiff in a situation where there are no court-approved interrogatories, you can often get information from the defendant much more quickly by means of a narrowly-crafted corporate-representative deposition notice, especially if the defense lawyer plans to tie you up for months with interrogatory objections.
By going straight to the corporate representative, you cut out the middleman (that is, the lawyer with the time-wasting objections to your interrogatories). Of course, you'll need to get records first, a step that will pose other opportunities for mischief by your opponent. But if you notice the deposition in advance while your records request is still outstanding, it can provide a sort of leverage to get things moving more quickly.