In economy it excludes front rows, extra legroom seats and similar. On European flights it's normally not a problem to choose these at T-48 (or even at check-in) as they rarely sell out in advance.

In business, all seats are standard seats on European flights. On longhaul it excludes some better seats like first row on A350 Opera seats (large open space instead of footwell) - although I was recently able to select them as a FB Silver, but that was probably a bug.