Prctically erasing better than overwriting alone since each write to an existing file on a SSD drive remaps the new write to a new recently erased flash sub-page and the previous contents are again queued for eventual erasure in future garbage collection. rendering it unrecoverable by labs accessing the flash memory chips directly.
Paul S, SSD dievices conencted directly to computer via SATA or other designed in busses under operating systems that support TRIM on a file by file deletion or partition deletion basis like Windows 7 or above, for instance, automatically practically erase deleted files data by de-allocating the flash memory sub-pages from access for the given LBA and logical clusters making the data imediatly inaccessible via the SSD firmware and queuing the pages for eventual perminant electrical erasure during periodic garbage collection by the SSD drives firmware. Note that some tools require the SSD to be disconnected from the PC/laptop & then reattached, &/or booting to a USB stick. Many companies use a disk shredding service to physically destroy discarded drives. That doesn't mean another user could access that remaining data, but an electronic tech might. The problem is that because not every block is easily accessible, you can't verify it worked - when tested several years ago on different brands & models of SSD, it did not always work. Some manufacturers offer their own tools for download, & you can use 3rd party tools like DoYourData Super Eraser. An SSD can however send a voltage spike to each block of storage resetting it to its initial state.
SSDs tend to use over-provisioning, which practically speaking means that you cannot access every block of storage to make sure it's cleared. Erasing or clearing data is a safeguard before selling or giving or throwing away a used conventional, SSD, or USB drive or memory card. That of course doesn't apply to an SSD since there are no write heads, but they still can be cleared or erased. Traditional erasing overwrites the data on a conventional hard disk, making multiple passes because the write heads wobble a tiny bit.