It might help with being understood, as in, they might forgive "weird" behavior more if you tell them, but there's also a chance you won't be allowed to join them if you tell them. That's what happened to me when I tried to do voluntary work and they found out about me being on the spectrum and about my physical disability. Of course, I can't say for sure if me being on the spectrum alone without the physical disability would've been a problem or not, or if the physical problem wasn't an actual problem but me being on the spectrum was, but the point is, sometimes people get shut out of doing voluntary work for these kind of reasons.
In a way, I do understand their decision; I would've been working with kids, so if something had gone wrong, there could've been a big mess with a lot of consequences... but honestly, I also feel like I was discriminated against a little. The official documents they got their hands on about my condition were almost a decade old, so while I still had the same conditions, lots of the problems they caused weren't up to date. But it turns out that what are currently facts don't really mean a lot if old facts are black on white and written by professionals.
The thing that annoyed me most about this was that they let me complete the training for this voluntary job and didn't even take the time during it to pull me aside and give me a heads up about there possibly being a problem with my conditions. Instead, they just called me a few weeks after it finished and told me that due to my conditions, I don't qualify. They'd had my papers for weeks, they'd met me several times after getting them, so not bothering to tell me face to face was an a** move in my opinion.
Of course, part of the fault lies with me in the sense that when I contacted them for the first time, I should've asked directly if me being disabled would be a problem. But since I didn't want to face any prejudices, I was more indirect and asked if there were any specific things that could prevent someone from getting to do this, and they listed stuff like criminal record and such, so I assumed a disability wouldn't be an automatic no no since it wasn't brought up on that listing... who knows, maybe it's not automatic, or maybe the person speaking never imagined that someone disabled would want to volunteer.
Anyway, sorry for hijacking the thread for a moment and making this about me. Some memories resurfaced and I felt like I needed to get this off my chest...