The point of it
The idea (from Paul Raper) is to be able to follow up a collocate by requesting a new concordance based on it, in the same text files as selected for the collocate. This aids exploration of related words.
How to do it
Here is an example, where there is a collocate list relating to BEERS. Select a word of interest, such as KEG,
and select Follow collocate in the Compute menu.
WordSmith starts up a new Concord window with a search on KEG.
The search is carried out on the most recently selected text files (selected using the file-choose window or by reading in a saved concordance).