If you specify COPY_ONLY for a full backup, it will not affect the following differential backups. I.e., the following differential backups will be based on the last full backup which was not performed with COPY_ONLY. Another way of looking at this is that a full backup using COPY_ONLY will not reset the DIFF (also known as DCM) page, which is page 6 and repeated approximately every 4 GB in each database file.
If you specify COPY_ONLY for a log backup, it will not affect the following log backups. I.e., the log backup chain will be without the one(s) produced using COPY_ONLY. Another way of looking at this is that a log backup using COPY_ONLY does not empty (truncate) the log.
That’s it! COPY_ONLY for a full backup does not, in any way, affect the restoreability for log backups.
The copy-only is a great feature, but understand what it does and how it works.