A scanned signature could be so handy, it will be put under the letter if the boss is not there. For some letters you can do that, for others it is not recommended, and for other types of writing simply not allowed.
Scanned signature: Not always allowed
For certain documents, the original signature is required by law, such as dismissals, severance agreements, employment certificates or surety bonds. For purchase and delivery contracts, offers and orders, the original signature is not required by law, but still recommended. At least when it comes to a contractual relationship for a longer period or orders with high monetary value. So you are on the safe side, if it should come to a lawsuit.
You can use a scanned signature in bulk mailings
For mass mailings, such as an advertisement, you can also use a scanned signature. In normal business correspondence, you should not do it because the recipient can easily see that the signature is printed.
No scanned signature on emails
For emails of all kinds (including applications) you should not use a scanned signature. The scan takes up unnecessary storage space and no one expects an autograph signature for an e-mail anyway. The typed name is sufficient.
Scanned signature: tip
If you use a signature scan on letters, make sure the printed signature looks good. Always scan them with high resolution. Print the signature in blue color, make sure it is an ink blue. If not, take black instead.