I dressed my older set of twin boys the same when little for a few reasons.
When clothes shopping it was just easier to pick up the clothes x2 as any task when you have twins needs to be quick before the feeding and changing needs to start again!
When at playgroups, soft plays read, parks etc it is easier to spot to the 2 children dressed the same, and so easier to round them up when they are heading off in different directions..... so for safety reasons.
One of the twins is like me, short, really dark hair, cuddly, dark eyes. All my other children are like Dp, tall blonde, blue eyes and people, strangers would always ask if he belonged to my family as he was the odd one out, as he got olderish he started to realise this and it made him feel sad, he 'wanted' to be like his twin brother through wearing the same things. ( we still get the comments now, and I reallllly wish people would say it out of ear shot. Maybe we are bring a bit sensitive but it does upset him. So dressing them the same made him feel part of the family when comments were made.
They look back at photos and argue (playfully) who suited what colour/outfit the best!
As for school, they were at a one class per year primary do were together, at secondary now and the school asked me whether to Seperate, I asked the boys and they wanted to be together. So they are and they are fine. The school will move them later on if problems arise. It's up to the twins. There is a special twin bond with my 2 and they make the decisions.
My other set are girl/boy. Obviously they were dressed different (and after 6 boys it was all pink, pink, pink for my daughter!) they constantly argue, same class at school because they have to be (will be split at secondary) and it's a living nightmare sometimes. They constantly ask/moan that they don't want each other as twins anymore!