Sometimes, depending on where your weed came from or how it was grown, you might see some seeds in the bag. When this happens, people always wonder if they can grow plants from bag seeds. The answer is, it depends.
You can always try to grow seeds you find in your bag. The presence of seeds means that some natural pollination has occurred, either from a nearby, undetected male plant, or from stray male pollen in female buds. The latter is more common as a female under stress can turn into a hermie.
If pollination was from a male plant, bag seeds will be more stable regular seeds and have a 50/50 chance of being male or female. If pollination was from male flowers from hermies, the seeds will be female, although will be prone to becoming hermies themselves if subjected to any stress. Hermies will produce seedy buds which could still produce bud that gets you high, but since energy goes to producing seeds they are usually less potent.
Bag seeds are always less stable than seeds bought from a breeder. Bag seeds typically have not been cared for and even if you follow best practices for germination, they might not germinate at all.
Pros of using bag seeds are that they are free, you already have them and you might get some decent bud. Cons of using bag seed are the unpredictability, the potential for producing Hermie plants (seedy buds which is probably how seeds got into your bag in the first place), the possibility of growing a male plant, and the potential for poor germination.
If you’re serious about growing quality plants, start with what you know are quality seeds from Mosca.