Uses and Abuses of Tablature
If you want to follow the fashion of the online guitar pundits, the thing to do at the moment is denounce "tab". It's an unnecessary crutch that stunts your growth as a musician, they say. Eat your greens and learn to read traditional notation instead!
Of course the reality is more complicated than that.
In summary, modern dots-and-lines notation is good at communicating "abstract" musical information such as pitch, rhythm and dynamics. Tablature is good at communicating specific decisions about how to execute those things on the instrument. Neither is good at doing what the other is good at, though each can be adapted if you insist.
Tab has got a bad name in the guitar community because of low-quality sites that offer "tabs" for songs by popular bands. These are often inaccurate of incomplete, and they can encourage bad habits in beginners -- I'll come back to that point in a moment.
Tablature is actually older than staff notation in its modern form, and was the standard notation used for lute, vihuela and chitarra music in the Renaissance. Nobody used dots and lines for this purpose, and even when they did tab was still in use. Bach, for example, wrote lute pieces in tab.
Here's a piece of lute tablature from c.1720:
Tablature provides different information from dots-and-lines notation. In the example above, the composer has indicated the rhythms above the tab staff, but this is pretty awkward to read.
For the opposite approach, here's a bit of a (different) classical guitar piece written out in modern, standard notation:
See the numbers and letters scattered all around the notes? Those are conveying fingering information (for both hands). Again, this is an awkward solution that forces a lot of information onto a single staff.
Personally I like to use both: a dots-and-lines staff with a tab staff aligned underneath. It helps that this is almost laughably easy to do in Sibelius.
For beginners, I admit tab poses a couple of dangers, but I think the right thing to do is mitigate them, not ban the whole thing.
First, if you want to work out a song, trying to do it by ear as much as possible is a great exercise. If you always run to a tab site, and then accept what you find there uncritically, then you're cheating yourself out of an opportunity to train your ears. Don't do that!
Second, relatedly, don't trust tabs you find on the internet -- assume there will be mistakes and use your ears to find and fix them.
Third, if you have some success learning songs using tab in conjunction with recordings you might feel that learning to read dots is a waste of time. Depending on your ambitions this might actually be true, but being able to read traditional notation is a valuable skill in many situations. Previous experience with tab will not make learning to read dots any harder.
Fourth, just because someone plays something one way doesn't mean you can't play it differently. Except under special circumstances (e.g. an exercise) tab should be taken as a suggestion, not the law. If it's more efficient or sounds better for you to play a part in a different position, for example, you should do that. Develop a critical attitude to tab: ask youself whether there's a better way to do it (for you).
I don't believe any of these are deal-breakers that means you should never use tab, or never show it to your students. It's a tool like any other; it can be used to advantage or abused to create poor results.