I am one of the two people in charge of our Venue & Hotel stuff, so I'm probably the best person to answer that for you.
I'm going to do what I do best and get more detailed than people usually ever ask for – so that's your heads up.
Yes we are sharing the convention center with other groups, yes this happens often, and no this isn't going to affect anything really.
We have never held the entirety of the convention center because even at BronyCon's highest attendance we have had more space than we knew what to do with. This year the space that we do have is:
Level 100: Hall A, B, C, D
Level 300: Rooms 301 - 326
And if I can say so myself, I think we did a good job of optimizing our use of the space for this year (it was no small feat, believe me).
CubingUSA Nationals are going to be taking place at the entirely opposite end of the convention center in a space we haven't used since 2013 (Camden Lobby and Hall G). They don't charge for spectators, so feel free to stop by and check it out! Be polite and mindful that they are not a convention but they are a competition so the vibe is likely very different.
The Law Conference going on on Wednesday is actually the annual LSAT exams that happen every year. They usually utilize the ballroom and one of the Halls.
Right around now if I were you I probably be thinking "I didn't ask for this, when the fuck are you going to answer the question?!" To which I would say "fair point, here you go"
Renting out the Baltimore Convention Center starts on Wednesday morning, and we usually start at about 6am between myself and the other person on our Venue & Hotel team and our General Service Contractor (we've been using Shepard for a while). All of Wednesday is setting up Level 100 which includes all the pipe and drape, all the kiosks, all the fixtures you see on Level 100 take a lot of labor to set up to our exact specifications. Besides that, our Operations team is sheparding our goods that we own or have rented over to the BCC in order to be organized and sent to their respective locations, including where our registration is. It then takes our registration team time to set up check in equipment, printers, networks. It takes time to organize badges, sponsor swag, etc. Set up on Wednesday is an all day affair, and that's only for registration on level 100. We have the vendor hall, the main panel hall (which has AV things that need setting up), and other things that need to be set up as well. We don't necessarily have access to set up on level 300 until first thing Thursday morning (again, that's how the contracts work) so setting up on 300 is going to be a long morning getting ready for attendees after they get their badges.
You might ask "why don't you just rent out some of the BCC on Tuesday?" and the answer always comes back to cost. It costs tens of thousands of dollars to do space rental. The BCC rents out their packages like ours for five days which is why we occupy the BCC from Wednesday through Sunday. The other cost comes from staff costs. The more staff we have to bring in early the more it costs in terms of things like lodging and the more it costs staff in terms of needing to take days off from work in order to volunteer sooner and sooner.
Wednesday being the day we have to do the majority of our set up means that a lot of people are working very hard to get everything ready, and I know our registration team is going to be working really hard in order to be ready for a hard open Thursday morning. We maybe might do a soft opening sometime Wednesday night, but it's nothing we can promise. We need to make sure the BCC is comfortable with it in terms of letting attendees through some doors rather than just BronyCon staff at later hours that we can't quantify, and most important of all our registration team needs to be okay with it. They need to not be exhausted from setting up all day and getting ready, they need to have eaten, and they need to be ready for an unknown number of people who might be around to come grab their badge early for a few hours.
Like I promised: a much more in depth answer than you probably hoped for or expected. Hopefully that's helpful toward understanding the "why"s of how things are set up. If I had to give you a tl;dr it would be "there absolutely is something else going on in the convention center on the 31st – it's BronyCon setting up getting ready to put on the event for everyone!"
Much love, and see you in August!
– Josh Dean