It all depends on the size and strength of the eruption. The Reykjarnes peninsula is relatively important, as it is home to Keflavik Airport on the north west tip, which is the main one serving the island and nearby capital Reykjavik. There is a cluster of towns around there and then Grindavik on the south side. However, the rest of the peninsula is mostly barren with volcanic rock fields (apart from the famous geothermal spa the Blue Lagoon somewhere in the middle and the power plant that provides its famous blue hot springs).

It so happens that this same area has seen eruptions in each of the last 2 years and apparently has a 10km stretch of underground lava flow still from that. I'm unsure if this implies it will be more or less impact full this time.

It appears that readings are centred on Grindavik. There's already been some road damage and land slippages there.