When a user forgets a password for a device (laptop, tablet, etc.), complete panic sets in because this horrific event often occurs at a critical time for the user (beginning of a presentation, going into a very important meeting, starting a video conference, etc).
Sometimes coworkers will step forward to calm the waters by quickly logging into the device as themselves, thus allowing the user to at least access the company network and hopefully get to critical items long enough to get through the important event at hand.
This is a practice that should be avoided at all costs. Your login and all activities associated with your login are a direct representation of you. All activity occurring under your login are your responsibility and there are no exceptions. Logging into a device, then handing that device over to another user and walking away is putting you and the data within your organization at risk. The other user may have the best of intentions but so many things can go wrong like: if they have network access that is lower than yours within your corporate infrastructure then they may accidentally see or manipulate confidential data and this puts both of you at risk as well as the data itself.