Can one manually, as well as safely, delete any of those dated - daily backup folders?
You can, but only by asking Time Machine to do it.
To do that, make sure you have an "Action" control in your Finder's toolbar. (It's there by default, but you may have deleted it. If the toolbar is showing controls as text, the text will be "Action". If toolbar controls are being displayed as icons, the icon will look like a gear. If it's not in the toolbar at all, use View→Customize Toolbar to put it back.)
Then, enter Time Machine (that is, the "star field" view). Navigate through time to the snapshot you want to delete. Then, from the Action control's menu, select "Delete Backup".
As of Snow Leopard, you cannot do this from Finder (by dragging a backup to the Trash), and you cannot even do it from the command line. Not even using
sudo. (Snow Leopard introduced a feature called Mandatory Access Controls, that even root is obliged to obey. Time Machine uses this feature to protect its backup; ONLY Time Machine is allowed to delete/rename/move/modify items within the backup.)
There are rare occasions where you want to delete a snapshot before its time. One is to influence which snapshots get promoted from hourly to daily to weekly. Just delete the other contenders that would beat out the one you want TM to promote.
(Example: you've been letting TM back up every hour, and notice that the snapshots it's promoting to weekly are all Tuesday snapshots. You have a daily snapshot, created on Thursday, containing files you created on Wednesday but deleted the following Friday. Those files were not incorporated into any Tuesday snapshots. If left to its own devices, TM will therefore not put them into any weekly snapshots. To force its hand, manually delete the Tuesday and Wednesday backups that don't contain the files, leaving the Thursday backup that does. Eventually, that Thursday backup will get promoted to weekly (it being 9 days after the previous weekly backup), after which TM will continue treating Thursday as the first day of the week, until the next time time there isn't a Thursday snapshot to promote.)
But for the most part, just leave TM alone. It can delete an old snapshot to make room just as fast as it can delete one you tell it to delete manually. You don't get any performance gain by fiddling with it.