Only if you care having daily events at the same time everywhere. For coordinating across countries it’s much easier to be all in the same timezones and just know that those to the east will wake, eat and so on earlier than those in the west, because there’s going to be differences anyway.
That’s my opinion after working internationally all my life.
Depends which side of EU. Same time for Spain and Poland makes little sense.
Spain should be GMT though, it’s quite literally below Greenwich.
Only if you care having daily events at the same time everywhere. For coordinating across countries it’s much easier to be all in the same timezones and just know that those to the east will wake, eat and so on earlier than those in the west, because there’s going to be differences anyway.
That’s my opinion after working internationally all my life.
Summertime makes sense for both