well, actually it's your own decision
I did not enable it by default because the "merge" tags in MAME were too often too wrong (pointing to wrong roms, just missing or holding bad checksums) in the past. cmpro can detect such errors during datfile parsing and fixes them, but still....I did enable the chd merge tags though...
For romsets, I actually also like to have the correct file names which otherwise get lost due to merging...but again, it's your personal taste....
I still wonder why people always come up with the set size argument. Comeon...HD space is cheap and if you're collecting MAME sets, you should not care about a minimum space gain by using the merge tags, full merging in general or 7z...
Last but not least....people should use this forum if they have questions/problems or may found a bug...it doesn't help when endless discussions are kept on a different forum. Normally I can fix issues within a day or two...when I know about them...when I got a scenario where I can easily repeat the problem...
Thanks for any support!