In England traffic roundabouts are usually when two busy roads cross each other and you want to have the traffic sort itself out rather than have traffic lights. They are quite often in South East England especially when two dual carraigeways cross, but also on a smaller scale in small towns when perhaps one road merges with another at an angle.

Mostly I've seen a logical reason for them.

In Finland they seem to be almost a mode item.

In the summer I drove in a small town called Jämsä. The main road by-passed the town and there was one roundabout on it for the benefit of feeder traffic. However when you got onto that much less important road (which also by-passed the town) with little traffic and unimportant roads joining it there was a sequence of another three roundabouts none of which seemed to have much point.

Where I live in Espoo (just outside Helsinki but still a built-up area) they are in the process of building two roundabouts.

One is a place that had traffic lights before (that never caused any problems) and is where two very minor roads join a slightly less minor road (which does get a reasonable amount of traffic). The traffic lights coped well enough except for maybe 15 mins a day ....   I doubt if the roundabout will help in that 15 or so mins.

The other is on the road near my house that *used* to - in parts (but not that part) - be full of traffic at rush hours but which nowadays (after a motorway addition got most of most of the cars) has been narrowed; made a 40kms zone (with a single speed bump at one end [but for both directions]); and so has much less traffic than ever before. That roundabout is being built where there are side roads leading to residential housing and where there have never been any traffic lights before - nor have they ever been needed.

It seems like the local council having done all the cycle lanes it can is now using its people (and my tax money) to do really unnecessary things.

Or maybe they are taking part in a non-publicised "who has the most unnecessary roundabouts in Finland" competition. They'll need a few more to beat Jämsä.