I don't put a divider between my wet and dry sections either. I just pile the gravel up just above what the max waterline will ever be and then lay my other substrate for land on top of that. IMO, it allows more area for the nitrobacter and nitrosomas to do their part in keeping your water chemistry correct. It also allows any plants you put in there to get water without you having to fuss over them. Plants also draw ammonia out of your water if their roots can get to it. Using divider also restricts how your shoreline runs so your "creativity" in building a unique environment for your fbts is narrowed.

I've had my 10 gallon tank this way for over five years. I don't have a filter, but I do change the water every week. No issues with water quality or funky smells have ever shown up.