Because the providers try to balance cell towers they may shift you to another tower which can cause a second or two of outage. Also if they get a lot of load on a particular tower the try to accommodate everyone which means everyone loses some data.
When I have watched people use mobile broadband to play games it works most the time maybe a couple times a hour you might get a lag spike. There is no way to predict this. If you have to have no lag spikes ever it is not a good platform to choose. The primary purpose is to provide internet access to people who are mobile so it is trade off between stability and mobility.
Pretty much I would not choose mobile broadband for a home internet connection if you have any other choice.