Frozen spinach is compact, convenient, and often much wetter after thawing than a handful of fresh leaves. That matters in a wrap, pastry filling, or thick sauce.
Cook or thaw it according to the packet. If the recipe needs a fairly dry filling, drain and press out excess liquid once it is safe to handle. For soup, that moisture may be less of a problem, so there is no reason to squeeze it automatically.
Use weight rather than trying to compare a frozen block with a vague handful of fresh spinach. Chop the cooked leaves if they remain in long strands that will be awkward to eat. Return unused frozen portions promptly to the freezer and follow the product's instructions rather than repeatedly thawing the whole bag for a small amount.