Depending on the facility and their rules, there may be a requirement (again, their rules) that they keep either two RNs or two licensed people on the floor. I have been at some that required at least two RNs on a unit (oncology), because their policy required to chemo certed RNs sign off on chemo. That may mean that if census drops, the CNAs will be sent home, then the LVNs.
This may not be fair, but since that is the rule of the hospital, and you chose to work there as an LVN/LPN, you have to bear it. As a traveler, I used to be first float....which meant that in some facilities, I would be floated 2 or 3 times in a 12 hour shift, and float for weeks on end. Is it fair....no. Is it smart, safe for patients, or make any sense(yeah, let's take the person who knows least about any floor here and move them 2-3 times a shift, for several shifts in a row)? But if I accept the job with the conditions, I have to deal, fair or not.
I will say that in facilities without those rules, I have frequently dealt with the RNs being sent off, LPNs kept (because they are cheaper) and been the only RN on the floor. Not good when you get injured midshift, and have to suffer through it because you cannot leave the floor.