For serious applications you need to keep a backup structure; e.g. one tape every night and these tapes are rotated, then every 7th one (say the Friday one) is taken out and placed into another rotating queue; then every last day of the month you take one out and place it into another rotating queue (that one will have 12 tapes in it), then you keep a tape of each year-end day, etc.
Various variously complicated backup schemes are used in different scenarios, the objective being that you can usually recover a tape from X days/weeks/months back but the further back you want to retrieve stuff from, the coarser the date resolution will be.
Obviously, the more recovery options you want the more tapes you need to have kicking around in your fireproof safe
And the bigger a safe you need, and the safe will probably cost as much as the tapes inside it. Fireproof safes for computer media (max internal temp +50C after +1100C outside for an hour, or whatever, plus watertight) are expensive.
Backup to flash is OK for up to a few gigs. Today it's quite cheap - a 2GB SD card is £10 on Ebay. But you could use a DVD just the same way. A double sided DVD is 9GB and they are notoriously unreliable in terms of read/write compatibility v. different brands of DVD drives.
The problem is when you want to backup more than say 9GB. Then tape is the only option, unless you are happy with just
one backup in which case you can use a removable (USB) hard drive, or some such.
The other issue is that modern operating systems (the hack called "windoze" especially) keep various files open all the time. These files cannot be accessed by other programs, so backup software needs to do various hacks to get at them. Usually this is done with a low level driver, and backup software comes with such hacks built-in. If these special files aren't backed up, then you cannot restore a whole PC HD from tape and have it working. Traditionally, only
tape backup software had the facilities for getting at these files. A lot of s/w can backup to CD/DVD now but this side is not well sorted and there are various issues.
Then you get the really complex stuff like backing up live databases and this needs yet more specialised software.
So.... you come back to tape, whether you like it or not. Like HD, mag tape has outpaced everything else in terms of sheer storage capacity per £ and continues to do so.
You also need to think long term. You can google for backup software and you will get a hundred products. I bet you 90 of these will not be around 5 years from now, so your old backups will not be accessible (the media format is nonstandard) unless you maintain a suitable original PC running somewhere.
The above reasons is partly why the awful hack called Backup Executive is still around.