The better the signal to noise the better the measurement. The next issue is how you excite the room. But if there is a lot of general noise in the room, you will need to use higher levels. Use the results of the measurements to guide you. For more detailed measurements some use portable speakers so they can excite the room from a particular place.
Microphone placement is important as well.
For general measurements it needs to be in the far field. Lower sampling rates will help with measurements at low frequencies. Keep good notes or use long file names to help you figure out what you were doing when you later analyze the data. Can't tell you how many times I made measurements thinking that I would remember what I had done only to come up with a blank later when I wanted to show someone what I had done. To give you some idea as to what is possible, I am able to do measurements with signal to noise ratios of 30 to 35 dB with audiences and classical music.