Portfolios for some kind of investors effectively balance asset investments with liabilities incurred. Think about a pension account, where the future liability of the pension payment represents the liability and the currently invested monies are the assets. I am sure you can think of other similar situations but I will illustrate regarding pensions below.
Input assumption for the liabilities resolve around how to estimate amount and timing of pension payments as well as death rates, future inflation and if you venture further out about political stability. Assumptions about assets may include credit risk and future return potential.The technical assumptions about return and event distributions may need to be considered.
Similarly constraints are usually applied to asset classes or industry sectors. But since pension plan sponsors may change these constraints they are basically assumptions. One may even assume at the outset, that the plan sponsors actually reduce, say, equity allocations as the plan matures. Such an assumption would affect the time commitment one would be ready to make for equity investments and possibly avoid some classes such a private equity all together.
Result interpretation in such a setting may not be trivial. Some results may be conflicting or assumptions may not be quantifiable. Therefore aspects such as comparing to similar situations, judgment and how to incorporate judgment transparently into an actual investment decision are some aspects for consideration. Interpreting the investment returns achieved is the second area that provides for a good deal of work. Think about situations where some part of the portfolio has no mark to market value such as with private equity. The plan sponsor may want to interprete time-weighted returns and the private equity portion likely only shows IRR returns. Questions on how to reconcile this would need to be addressed.
Since the above cannot be exhaustive, for further illustration you may look at investment policy statements of pension plans (see this example)