This question sort of spoils a lot of the movie, so I'm just going to spoiler tag the whole question.
The heist that they plan is well-thought-out, and they try to cover every angle. Dr. Pym is a genius, and Hope has almost limitless access to the facilities, so they do a good job with the planning stage. They need to secure the Yellowjacket suit and formula, as well as destroy any backup data on the research. Part of the plan is to have Hope and Kurt wipe all the data from the servers, which worked. However, the execution of getting the suit gets spoiled at the last second (it is a movie after all). Things kind of go crazy, and Cross gets away with the suit.
During their escape from the building, they pull the fire alarm to get everyone out of the building before charges which the ants set go off. This seems like a bad idea, because it was the big reveal of the tech, so lots of people would have been there, making evacuation difficult. This also seems redundant, because they went through all the trouble and risk of wiping the servers just to have a black hole appear in the middle of the building, literally sucking every piece of it into nothingness.
I've only seen it once, but I don't remember why they set the charges. Honestly it seems like it would have been safer to just go in with the ants to set the charges and pull the fire alarm. The backups and the suit would have been destroyed, and the risk would have been lower. Basically Hope could just walk in, lower the water pressure to allow Scott in, pull the fire alarm, and watch the fireworks. Was there any reason for setting the charges to blow up the building?