AFAIK, most snippet expander apps use the clipboard to do their thing. Certainly Text Expander does.
The delay is how long Alfred (or TE) waits before restoring the previous clipboard contents (to allow enough time for the simulated paste event to succeed with the snippet contents). In TE, the delay is configurable and (IIRC) has a more aggressive (i.e. shorter) default. Or you set a shorter delay yourself a long time ago (as I did).
If the delay is too short, the previous clipboard contents might be restored before the paste event succeeds, thus inserting the clipboard contents instead of the snippet (the opposite of the issue you're having).
IMO, the delay should definitely be configurable, as some machines are much faster than others. With a non-configurable delay, Alfred has to be very conservative to ensure snippet expansion works on slow Macs.
