I know there are myriad reasons for aliases, many (most?) not good, but if someone can give me a simple explanation of when and why they make GOOD use of them (if that happens) I'd appreciate it.

The bad reasons I've heard so far are:
-LE
-other providers trying to mess with you
-hobbyists trying to mess with you
-LE
-LE

I don't see guys based on just a TER handle unless he's whitelisted, even then I try and get p411, date-check, references from girls or agencies etc...as backup/supplemental screening

the acceptable reasons for using alias are listed in the self help center.   I primarily use an alias to add humor to my posts.   I frequently post and discuss LGBT issues on the TS board, so I ironically use this handle for that purpose (Dr. Dobson is a right-wing homophobic evangelical hate monger on the radio).   When I was new, I was a little insecure about my sexual preference and I used another alias to ask questions.  Both of these reasons are acceptable according to the policy and in my opinion, "Good" reasons for using an alias.

When I first came to TER I had issues with my wife's job as a provider. I wanted to post about some of the issues I was having yet didn't want the world to know my wife did other men for money. Aliases allowed me to do this. Privacy is important and aliases allow for additional privacy.

As indicated in this string - there are very valid reasons for people using them.  

One of the reasons that I HATED it is because people would use them to flame others for no apparent reason.  Board moderators are really good about not having this happen as much anymore.

so as not reflect on issues I might have been discussing which had nothing to do with the gentle ladies I have reviewed in the past.  Neither your TER handle (review name) not alias are (hopefully) your given name.

Sometimes a hobbyist is looking for information regarding something that might be taboo or embarassing or "against the norm" of the normal community. Example I saw someone not too long ago (I forget where) post that he was looking for I believe a provider w/ a male friend who would be willing to use a strap-on on him in a MFM. While I could honestly care less what he's into, he might have been afraid (or just not willing to deal with) some of the responses he might have gotten.

Or perhaps a hobbyist or provider was involved in a situation and wants to alert the board of what happened w/o sacrificing his identity which may cause some type of backlash or retaliation against him.

Could also have been involved in a negative experience and simply looking for advice on how to handle it.

To amplify and/or accentuate the sarcasm, humor, etc of his post or reply.

There are a few good reasons why one might use an alias. But with anything of course there are going to be those who abuse it's power and use it for purposes not intended for. It comes w/ the territory and just something you have to deal with. Although if someone is REALLY taking liberty with it in an above-and-beyond way the mods have flipped the alias and shown the posters true handle before.