Two blobs were pressed together during testing. This has removed the washer.
Since then, the blobs have been flawless without any problems.
Can I leave it like that? Or what is the function of the washer?
The washer prohibits the blob from transferring to the nozzle and being carried to the print. In our testing we saw that occasionally that could happen.
If you are getting perfect blobs then it may be fine to leave it off. However, you should be able to recover the washer and reshape it with some needle nose pliers. If you were having issues with the blobs being improperly formed with the washer in place then that indicates there is another issue.