- you may touch everything, often including things inside the computers itself
- the people working there (or, as is often the case, the one guy working there) is knowledgeable, willing to talk about it in depth, cares, and you can have a real conversation with them.
- there's a lot of surprising hardware around I had no idea existed (from failed computer companies, to specialized I/O of decades past, to special-purpose hardware)
You cannot get the same full experience with most regular museums, as then you have to follow their narrative instead of following your curiosity.
On the other hand, these museums are often not much more than an erudite collection of historical artifacts they got their hands on. To preserve is to select with a plan, not just collect everything.