I can see a few advantages:

Internal Propaganda. You show to your own people, that you can cut off the enemies' communication lines easily.

External Propaganda. You show to the enemies that they are vulnerable, spreading fear and doubt in their own strength.

Exercises for larger operations. You train ships' crews for those kinds of maneuvers, in case you need to to it a large number of times, e.g. to cut off all baltic cables at once, cut all transatlantic cables, cut all cables to some important island like Iceland, etc.

Internal Normalisation. You get the ships' crews, your population and your governance structures used to a more aggressive mode of operations.

External Normalisation. You get the enemies' population and governance structures used to those kinds of pinpricks. So when the large-scale operation starts, they will ignore the first signs as "just the usual irrelevant pinpricks".

Testing and mapping connectivity. When the cable goes down, you can have your spies look at which relevant infrastructure goes down at the same time.

This is one of the best, succinct lists of motivations for hybrid warfare i've seen.

But i could suggest another potential benefit for russia: If russia already operates under the assumption that they are in a (cold) war with EU/NATO, and they don't care about the effects on the relationship with Finland. Then this may simply be a really low cost, high damage operation. That not only imposes the replacement cost of the cable, but also forces countries to invest in counter measures.

Testing the response.

One day they might send 20 ships all at once to cut all overseas cables in one go, and it won’t seem like the preparation for an invasion but just another provocation.

By that same morning they start the invasion of Estonia / the Baltics and separated them from the world through communications jamming and cutting all overseas cables. Without NATO support the Baltics are ocuppied by the same afternoon. In 12-16 hours Rússia has essentially re-occupied them.

These normalisation exercises are a part of it.

Well, Putin doesn't always follow logic. Logically, all these provocations make Europe more united. But in his mind he's probably doing some kind of force projection and punishment for supporting Ukraine.