Basically there are two main reasons for that. One of them is that if you choose to go with reversed incremental mode then you will have to copy entire VBK file every time. This file contains full backup of the most recent state of your VMs. If you only do tape dumps weekly or even more rarily, this does not matter. However, if you need to backup to tape daily, this may cause some issues. However, if you're able to offload entire VBK file to tape during your tape backup window, and have enough tapes to accommodate dumping full backups to tape daily, then reversed incremental mode should be a good choice.
On top of that, please be aware that forward incremental mode should give you better incremental backup performance rates due to the fact that with forward incrementals you'll have three times less I/O, and thus much lower IOPS during incremental runs (but of course, you still have to pay the price during periodic full backup, which is typically for weekend though). The same refers to offloading backup files to tape, as only incremental changes (VIB file) should be transferred to tape, so backup to tape will go much faster.
Hope this makes sense.