There are now very effective treatments for psoriasis to the point that most patients can be clear or nearly clear of the disease. These range from UVB light therapy to drugs such as methotrexate and ciclosporin and a growing number of monoclonal antibodies such as adalimumab. Clearly these treatments do have some small risk attached so there is a trade off between how greatly the psoriasis is concerning you and the (small) potential for side effects. You can discuss this trade off in detail with your dermatologist.
While YMMV, from a patients perspective, with severe psoriasis and psoriatic arthritis, you want to get to biologics as quickly as your healthcare system (or budget if you have fu money) will allow.
Insurance companies love methotrexate because it is cheap. It has a far higher NNT than the biologics, is less effective at clearing psoriasis, and has horrible side effects.
COI: Dermatologist