They slightly reduce the distance and amount of infected moisture from your lungs spreading into the surrounding air a bit as you exhale, but that's pretty much the extent of their benefit. Not enough to matter, though, as evidenced by that CDC study.
Masks have always been to protect others from you.
If they don't stop incoming viruses...
They don't magically stop them from getting out.
Even the CDC says they are of no help.
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article
They slightly reduce the distance and amount of infected moisture from your lungs spreading into the surrounding air a bit as you exhale, but that's pretty much the extent of their benefit. Not enough to matter, though, as evidenced by that CDC study.