Maybe a bit confusing from the title, but I will try. For example say you start with a sphere and you more or less make that in to a head. Rather than use a cylinder or a sphere to form a neck and then use the merge tool, you could use the clay brush to add geometry and build up a neck. Hope that makes sense.
You need to turn on Dynamic Topology, which will add new vertices when you’re sculpting - otherwise you’re just manipulating the same vertex’s and straining their boundaries even more. Once that’s enabled, Clay tool - and also Layer - builds up new surface mesh just lovely 
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I think you confuse sculptris pro (dynamic topology in Nomad) with clay buildup (accumulate option in stroke menu for clay, enabled by default).