Merge by Selected Changesets
When you want to merge and use the option Merge by "Selected Changeset" it extracts the changesets which is due for merging.
Currently setup only allows you to select the changesets continuosly (based on date) and wont have option to select particluar changesets.
For instance: You have changesets 1,2,3,4,5 due for merging from Branch A to B. You only get an option of merging 1,2,3 or 2,3,4 etc but not 1,3,5 (not merging 2 & 4).
This is particularly required when you are merging from dev branch to production branch, where you would want to avoid redundant/ backed-out changesets being merged. Leads to repetation of work.