Typically, if you care about recovering your data after a disaster in an acceptable amount of time, full backups are done regularly (weekly, bi-weekly, whatever) and incrementals or differentials are done daily. Differentials will allow you do do a full recovery in three steps:
Restore the latest full (which will only be a week or two old).
Restore the latest differential.
Go have a snack.
Incrementals will require you to restore every single tape since the last full backup was taken. This is not a good thing if you just have never-ending incrementals.
Also, keep in mind that backups stored on-site are subject to destruction in a disaster just like your servers are (flood, fire, angry ex-employee). Send them off-site. Send them off-site regularly. Tape rotations are quite common.
I have about 200 tapes in my rotation right now. We use about 12 for a full every weekend, and between 3-5 per day for the differentials. We have 5 tape "sequences" that are basically a week long. Every day a courier picks up the day's tapes and brings back a box from 5 weeks ago. The only tapes that we keep on hand are what we need for the week's backups. Everything else is off-site in a hardened facility, in a fireproof case. This is the only way to do it if you want to recover from a disaster.
When the tapes return from the DR facility and are fed to the hungry tape robot, they're added to the scratch pool and are overwritten. At most, I will only ever lose a day's worth of data and I can go back as far as 5 weeks if necessary. There are other policies for certain things that legally need longer retention, but that's another story and they're the exception not the rule.
Of course disk-to-disk is good too for quick restores, but offite archives are a must for DR.
tl;dr - Most people don't just use the same few tapes over and over. The best way to do things if you care about archival recovery in the event of a disaster is to have multiple tape sequences that are cycled off-site, and just overwrite the oldest when they come back unless you have a legal reason not to.