Manual Trashing of older TM backup files

Question

My question is somewhat related to another topic at
http://discussions.apple.com/thread.jspa?threadID=2445257&tstart=0
but here goes anyway. I have TM backup partition on external drive and
it is getting full. I know TM will toss old backups as needed; however, I
would like to use the finder to open the backup and manually delete
several of the older backups to gain some disk space.
Anything wrong with just trashing some of older backup that are no
longer needed?

Answer 1

Yes. If you do that it will mess up the TM backup. Use the TM application only to remove individual files from a TM backup.
If you backup disk is too full and you've received the disk full alert, then replace the backup drive or erase it and start over.
A TM backup drive should be at least twice the capacity of the drive it backs up. If it is then you will be unlikely to see a disk full alert. See:
About TM "Backup Drive is Full" Alert
TM only deletes older files if they have been deleted from the source and when TM needs space on the backup drive for a new incremental backup. Time Machine "thins" it's backups; hourly backups over 24 hours old, except the first of the day; those "daily" backups over 30 days old, except the first of the week. The weeklies are kept as long as there's room.
So, how long a backup file remains depends on how long it was on your Mac before being deleted, assuming you do at least one backup per day. If it was there for at least 24 hours, it will be kept for at least a month. If it was there for at least a week, it will be kept as long as there's room.
Note, that on a Time Capsule the sparsebundle grows in size as needed, but doesn't shrink. Thus, from the user's view of the TC it appears that no space has been freed, although there may be space in the sparsebundle.
Once TM has found it cannot free up enough space for a new backup it reports the disk is full. You can either erase the backup drive and start your backups anew or replace the drive with a larger drive.