I'm a submissive that needs structure. Submissives all around will identify with either discipline, obedience, structure or rules or perhaps more than one. With structure can come rules and that's how my submission runs in our dynamic. I serve my Master by following his rules that govern the structure of my day. It works best for me and we are both happy.
So what is structure? Structure is an organized framework for your routine. It can be decided upon for exactness or you can have a more flexible structure that allows you some freedom for decision making. For example, if your owner decided that there would be structure to how you were to prepare for bed, he may set up rules that tell you when to go to bed, how to get into bed and what to wear to bed. The structure of this routine is important to defining your submission and the value of your service. Structure can also be more flexible to let you decide how to go about the routine. If your owner only gives you a bedtime, then it is assumed that you will set up a routine leading up to bedtime so that you aren't going from eating dinner straight to bed.
Rules are the backbone of structure. They provide the correct way to do things within the structure established.Some submissives have a lot of rules and others have very few. This is decided upon how flexible the structure of the relationship is. It is not necessarily better or worse to have a lot or a few rules. The only thing that matters is if you follow them correctly.
Is structure present in every relationship? Sure on some level, there is structure in every relationship, vanilla or otherwise. In a D/s context, the structure may be more pronounced if it exists. Bedroom submissives tend to have less structure than 24/7 submissives and slaves likely have even more than that.
What is your structure like? Is the framework your rules map out really well defined or do you have some liberty to improvise to get the job done?