Free-seating actually helps avoid trim problems rather than causing more. There are a number of key points when comparing free-seating to allocated from a trim point of view:
1. The trim envelope will be 'narrowed' as a result of a free-seating policy, therefore giving a better margin for error than an allocated seating operation.
2. Passengers will generally tend to spread themselves reasonably well through the cabin on a free-seating operation.
3. It is immediataely clear visually if there is a major imbalance of pax spread in the cabin, whereas you can't tell if pax have moved on an allocated seating flight......unless you cross-check all the seat allocations.
4. Most/many loadsheet systems do not account for the trim difference due to sex or adult/child differences. On a 2-class operation, the front-end is more likely to be a heavy Adults/males mix, with a greater proportion of children at the rear of the cabin.....but the loadsheet is very likely based on "15 in Bay A and 15 bay C" having a very similar trim affect. Single-class / free-seating helps eliminate this, as Males/Females/Children will probably have an even spread throughout the cabin.
Free-seating has it's problems, and may not be popular from a consumer perspective, but for trim purposes I believe it has a number of safety advantages and is less prone to gross error.
In trim