Is Sustaining a spell optional for some spells?

[Datak Akhana]

I understand that some spells have a duration like "sustained up to one minute," meaning that the spell lasts as long as it is sustained, with a maximum duration of one minute.

If the spell has a fixed duration but the description says it can be sustained, does the spell need to be sustained to keep it up? For example, Bless has a duration of one minute. The description says, in part, "Once per round on subsequent turns, you can Sustain the spell to increase the emanation’s radius by 10 feet." If I don't Sustain it, does Bless drop or just stay at whatever radius it was when I stopped Sustaining?

[Dr. Frank Funkelstein]

Bless has a duration of 1 minute. If you use the Sustain action, you expand the radius. If you don't, it stays as it is. It does not influence the duration.

[Finoan]

Glamorize is an even better example of this.

The duration alone lists how long the spell will last. A duration of Sustained means that the spell needs to be sustained each round or else it will end. A fixed duration will last its fixed duration, even if there is an effect that happens if the caster chooses to spend an action on Sustain.

[Ravingdork]

I concur. Fixed duration spells last their full duration, whether you sustain them or not.