Anyone can pick their Y seats when they make a booking. However some seats are not released by the airline until the last minute at check-in (bulkhead, front rows etc.) unless you have special requests such as tight transfers, babies, or upper-tier FFs.

The benefit you will get from the Elite/SE tier is blocked seats. AC will block out the seat next to you if pax loading permits. Happens to me all the time flying to & from HKG.