My initial answer failed to consider that everyone has a varying level of base fitness, hence the revisions. Assume that you can do some intervals or faster riding safely during the commute, including safely for other traffic. For less trained cyclists, there may be enough road to improve your fitness if you push things a bit on the commute. A 17k daily commute isn't a huge amount of road, so this won't carry you to a high fitness level. But this may be OK for your needs! More discussion follows.
Consider the pyramid above. It's a conceptual model by sports scientist Stephen Seiler, based on Maslow's hierarchy of needs. I obtained the image from 80/20 Endurance, which discusses training in more detail.
Seiler's proposition is that if you just focus on total volume - ride up grades, as Eddy Merckx is thought to have said - this will improve your performance, but you will hit a plateau at some point. Past that point, you need to add intensity to keep improving.
However, depending on your goals and your current fitness, this may or may not be a problem. Certainly, if the alternative is doing nothing, then doing anything within reason (be safe, don't overtrain) will improve fitness. Note that to reduce cardiovascular risk and improve general health, you don't need a whopping amount of physical activity. The American College of Sports Medicine and similar bodies just recommend some moderately intense physical activity for at least 30 minutes on most days of the week (5, in the ACSM's case), plus some muscle strengthening days. Moderately paced walking counts as sufficient intensity for this purpose.
If you want to maximize your fitness and do structured intervals, there's not enough time on this commute. We would usually do a 5 minute warmup or a bit more, then the work sets, then a cooldown at the end. For example, for VO2max workouts, riders should usually work up to 16-20 total minutes at VO2max power, perhaps more. For sweet spot (~90% of FTP), I think experienced cyclists want to start with a total of 40-45 minutes in zone and work up from there, with time in zone a bit less for threshold intervals. There is no way to do that much in 17 km while also stopping for lights and being sure not to menace parents, children, and dogs.
A short commute may be a reasonable place to do some anaerobic intervals, other users permitting. Those are something like 30-90s sprints, then easy pedaling. Anaerobic capacity is useful on competitive group rides. You wouldn't want to do these every day, as they can get tiring. Also, I think the gains to aerobic fitness should be limited.
In theory, it would be more effective to take the commute at zone 1 or 2 (recovery or endurance pace) and set aside some time to do structured intervals, or find a group ride that is challenging for you, or do the same thing on longer solo rides. If you're already doing that, then you most likely want to keep the commute easy, probably recovery pace.
I'm answering from the perspective of a fairly experienced cyclist. 30-40 minute structured workouts are generally not enough to drive adaptations for me at my current fitness level. That said, everyone is at a different place. So you could consider where you currently are in building an overall workout plan.
Explanation of the pyramid
If you are starting from a low base, just cycling more is sufficient to progress.
To progress from there, you need to add intensity. In particular, add intensity near or above your functional threshold power. Riding tempo is not quite hard enough to drive good adaptations. If you don't overtrain, just adding intensity in an unstructured format will produce gains. Road pros used to race themselves into shape. Or you could just do group rides.
To progress from there, you need to pay more attention to intensity distribution. In particular, you want to make sure you do enough work at high intensity, and the balance of your work needs to be at endurance or recovery pace. There are a few intensity distribution schemes out there, e.g. pyramidal or polarized training. You can Google these, but the basic precept is to start paying attention to how much time you're spending at intensity, and increasing that time gradually. For example, at my experience level, about 45 minutes of sweet spot or 40 minutes of threshold is the lowest I would aim for in a session. The more complex techniques above this tier offer diminishing returns (says Seiler) and are also more complicated to pull off, so a lot of people would benefit from professional help here.
My intuitive sense is that the majority of riders don't necessarily need to even get to step 3 to achieve enough cycling fitness to gain satisfaction. Obviously, this doesn't mean they should not do so, or that it's wrong to want to maximize performance. It's more that it may not be necessary. I think most fit adults can complete a century just by focusing on volume.
I have not vetted the evidence base. My understanding is that Seiler is generally well-regarded. No researcher is perfect. I suspect that he's generally on point, but in principle anyone can be wrong on something, or the field can consider something well-accepted when it's actually wrong, like narrow high-pressure tires.